erofs: fix potential overflow calculating xattr_isize

Given on-disk i_xattr_icount is 16 bits and xattr_isize is calculated
from i_xattr_icount multiplying 4, xattr_isize has a theoretical maximum
of 256K (64K * 4).

Thus declare xattr_isize as unsigned int to avoid the potential overflow.

Fixes: bfb8674 ("staging: erofs: add erofs in-memory stuffs")
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230414061810.6479-1-jefflexu@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/internal.h

@@ -304,7 +304,7 @@ struct erofs_inode {
 
 	unsigned char datalayout;
 	unsigned char inode_isize;
-	unsigned short xattr_isize;
+	unsigned int xattr_isize;
 
 	unsigned int xattr_shared_count;
 	unsigned int *xattr_shared_xattrs;