jfs: Use unsigned variable for length calculations

jfs: Use unsigned variable for length calculations

To avoid confusing the compiler about possible negative sizes, switch
"ssize" which can never be negative from int to u32.  Seen with GCC 13:

../fs/jfs/namei.c: In function 'jfs_symlink': ../include/linux/fortify-string.h:57:33: warning: '__builtin_memcpy' pointer overflow between offset 0 and size [-2147483648, -1]
[-Warray-bounds=]
   57 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^
...
../fs/jfs/namei.c:950:17: note: in expansion of macro 'memcpy'
  950 |                 memcpy(ip->i_link, name, ssize);
      |                 ^~~~~~

Cc: Dave Kleikamp <shaggy@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: jfs-discussion@lists.sourceforge.net
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Jeff Xu <jeffxu@chromium.org>
Message-Id: <20230204183355.never.877-kees@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>