xfs_scrub: fix complaint about uninitialized ret

xfs_scrub: fix complaint about uninitialized ret

Coverity complained about the uninitialized ret in run_scrub_phases.
It's not sophisticated enough to realize that phase 1 and 7 are both
marked mustrun and are never the repair or datascan dummies and that
therefore ret is always initialized by the end of the for loop, but
OTOH there's no reason not to fix a trivial logic bomb if that ever
changes.

Coverity-id: 1455255
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>