There is no need to dip into reserve pool. Reserve pool is used for much
more important things. And xfs_trans_reserve will never return ENOSPC
because punch hole is already done. If we get ENOSPC, collapse range
will be simply failed.

Cc: Brian Foster <bfoster@redhat.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>