udf: Fix -Wstringop-overflow warnings

Use unsigned type in call to macro min_t(). This avoids confusing the
compiler about possible negative values that would cause the value in
_len_ to wrap around.

Fixes the following -Wstringop-warnings seen when building ARM
architecture with allyesconfig (GCC 13):
fs/udf/directory.c: In function 'udf_copy_fi':
include/linux/fortify-string.h:57:33: warning: '__builtin_memcpy' specified bound between 2147483648 and 4294967295 exceeds maximum object size 2147483647 [-Wstringop-overflow=]
   57 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^
include/linux/fortify-string.h:648:9: note: in expansion of macro '__underlying_memcpy'
  648 |         __underlying_##op(p, q, __fortify_size);                        \
      |         ^~~~~~~~~~~~~
include/linux/fortify-string.h:693:26: note: in expansion of macro '__fortify_memcpy_chk'
  693 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
      |                          ^~~~~~~~~~~~~~~~~~~~
fs/udf/directory.c:99:9: note: in expansion of macro 'memcpy'
   99 |         memcpy(&iter->fi, iter->bh[0]->b_data + off, len);
      |         ^~~~~~
include/linux/fortify-string.h:57:33: warning: '__builtin_memcpy' specified bound between 2147483648 and 4294967295 exceeds maximum object size 2147483647 [-Wstringop-overflow=]
   57 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^
include/linux/fortify-string.h:648:9: note: in expansion of macro '__underlying_memcpy'
  648 |         __underlying_##op(p, q, __fortify_size);                        \
      |         ^~~~~~~~~~~~~
include/linux/fortify-string.h:693:26: note: in expansion of macro '__fortify_memcpy_chk'
  693 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
      |                          ^~~~~~~~~~~~~~~~~~~~
fs/udf/directory.c:99:9: note: in expansion of macro 'memcpy'
   99 |         memcpy(&iter->fi, iter->bh[0]->b_data + off, len);
      |         ^~~~~~
  AR      fs/udf/built-in.a

This helps with the ongoing efforts to globally enable
-Wstringop-overflow.

Link: https://github.com/KSPP/linux/issues/329
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

fs/udf/directory.c

@@ -95,7 +95,7 @@ static int udf_copy_fi(struct udf_fileident_iter *iter)
 	}
 
 	off = iter->pos & (blksize - 1);
-	len = min_t(int, sizeof(struct fileIdentDesc), blksize - off);
+	len = min_t(u32, sizeof(struct fileIdentDesc), blksize - off);
 	memcpy(&iter->fi, iter->bh[0]->b_data + off, len);
 	if (len < sizeof(struct fileIdentDesc))
 		memcpy((char *)(&iter->fi) + len, iter->bh[1]->b_data,