xfs: clear PF_NOFREEZE for xfsaild kthread

Since xfsaild has been converted to kthread in 0030807c, it calls
try_to_freeze() during every AIL push iteration. It however doesn't set
itself as freezable, and therefore this try_to_freeze() will never do
anything.

Before (hopefully eventually) kthread freezing gets converted to fileystem
freezing, we'd rather mark xfsaild freezable (as it can generate I/O
during suspend).
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_trans_ail.c

@@ -497,6 +497,7 @@ xfsaild(
 	long		tout = 0;	/* milliseconds */
 
 	current->flags |= PF_MEMALLOC;
+	set_freezable();
 
 	while (!kthread_should_stop()) {
 		if (tout && tout <= 20)