asm-generic: Use __BITS_PER_LONG in statfs.h

<asm-generic/statfs.h> is exported to userspace, so using
BITS_PER_LONG is invalid.  We need to use __BITS_PER_LONG instead.

This is kernel bugzilla 43165.

Reported-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1335465916-16965-1-git-send-email-hpa@linux.intel.com
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: <stable@vger.kernel.org>

include/asm-generic/statfs.h

@@ -15,7 +15,7 @@ typedef __kernel_fsid_t	fsid_t;
  * with a 10' pole.
  */
 #ifndef __statfs_word
-#if BITS_PER_LONG == 64
+#if __BITS_PER_LONG == 64
 #define __statfs_word long
 #else
 #define __statfs_word __u32