xfs_scrub: in phase 3, use the opened file descriptor for scrub calls

xfs_scrub: in phase 3, use the opened file descriptor for scrub calls

While profiling the performance of xfs_scrub, I noticed that phase3 only
employs the scrub-by-handle interface.  The kernel has had the ability
to skip the untrusted iget lookup if the fd matches the handle data
since the beginning, and using it reduces the phase 3 runtime by 5% on
the author's system.

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