xfs_scrub: reduce fsmap activity for media errors

xfs_scrub: reduce fsmap activity for media errors

Right now we rather foolishly query the fsmap data for every single
media error that we find.  This is a silly waste of time since we
have yet to combine adjacent bad blocks into bad extents, so move the
rmap query until after we've constructed the bad block bitmap data.

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>