xfs: fix returned valued from xfs_defer_can_append

xfs: fix returned valued from xfs_defer_can_append

xfs_defer_can_append returns a bool, it shouldn't be returning
a NULL.

Found by code inspection.

Fixes: 4dffb2cbb483 ("xfs: allow pausing of pending deferred work items")
Cc: <stable@vger.kernel.org> # v6.8
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Acked-by: Souptick Joarder <souptick.joarder@hpe.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>