Fill in cn_name in struct consdev.

It makes debugging easier if the name is filled in from the start.

Reviewed by:	imp
Sponsored by:	https://www.patreon.com/cperciva
Differential Revision:	https://reviews.freebsd.org/D35795

sys/sys/cons.h

@@ -104,6 +104,7 @@ extern	struct tty *constty;	/* Temporary virtual console. */
 	static struct consdev name = {					\
 		.cn_ops = &ops,						\
 		.cn_arg = (arg),					\
+		.cn_name = #name,					\
 	};								\
 	DATA_SET(cons_set, name)