xfs: really fix the cursor leak in xfs_alloc_ag_vextent_near

commit e3a746f5aab71f2dd0a83116772922fb37ae29d6 upstream.

The current cursor is reallocated when retrying the allocation, so
the existing cursor needs to be destroyed in both the restart and
the failure cases.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Tested-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>