dm ioctl: fix error return code in target_message

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: 2ca4c92f58f9 ("dm ioctl: prevent empty message")
Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Qinglang Miao <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>

drivers/md/dm-ioctl.c

···
 
 	if (!argc) {
 		DMWARN("Empty message received.");
+		r = -EINVAL;
 		goto out_argv;
 	}