dm mpath: add m->hw_handler_name NULL pointer check in parse_hw_handler()

Avoids false positive of no hardware handler being specified (which is
implied by a NULL m->hw_handler_name).
Signed-off-by: tang.junhui <tang.junhui@zte.com.cn>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -1002,6 +1002,8 @@ static int parse_hw_handler(struct dm_arg_set *as, struct multipath *m)
 	}
 
 	m->hw_handler_name = kstrdup(dm_shift_arg(as), GFP_KERNEL);
+	if (!m->hw_handler_name)
+		return -EINVAL;
 
 	if (hw_argc > 1) {
 		char *p;