xfs_quota: drop pointless qsort cmp casting

xfs_quota: drop pointless qsort cmp casting

The function cast in this call to qsort is odd - we don't do it
anywhere else, and it doesn't gain us anything or help in any
way.

So remove it; since we are now passing void *p pointers in, locally
use du_t *d pointers to refer to the du_t's in the compare function.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>