xfs: hoist the already_fixed variable to the scrub context

xfs: hoist the already_fixed variable to the scrub context

Now that we no longer memset the scrub context, we can move the
already_fixed variable into the scrub context's state flags instead of
passing around pointers to separate stack variables.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>