dm log: use PTR_ERR value instead of ENOMEM

It's nicer to return the PTR_ERR() value instead of just returning
-ENOMEM.  In the current code the PTR_ERR() value is always equal to
-ENOMEM so this doesn't actually affect anything, but still...

In addition, dm_dirty_log_create() doesn't check for a specific -ENOMEM
return.  So this change is safe relative to potential for a non -ENOMEM
return in the future.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-log.c

@@ -455,7 +455,7 @@ static int create_log_context(struct dm_dirty_log *log, struct dm_target *ti,
 			r = PTR_ERR(lc->io_req.client);
 			DMWARN("couldn't allocate disk io client");
 			kfree(lc);
-			return -ENOMEM;
+			return r;
 		}
 
 		lc->disk_header = vmalloc(buf_size);