arcnet: com20020-isa: Mark expected switch fall-throughs

Mark switch cases where we are expecting to fall through.

This patch fixes the following warnings:

drivers/net/arcnet/com20020-isa.c: warning: this statement may fall
through [-Wimplicit-fallthrough=]: => 205:13, 203:10, 209:7, 201:11,
207:8

Reported-by: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/arcnet/com20020-isa.c

···
 	switch (ints[0]) {
 	default:		/* ERROR */
 		pr_info("Too many arguments\n");
+		/* Fall through */
 	case 6:		/* Timeout */
 		timeout = ints[6];
+		/* Fall through */
 	case 5:		/* CKP value */
 		clockp = ints[5];
+		/* Fall through */
 	case 4:		/* Backplane flag */
 		backplane = ints[4];
+		/* Fall through */
 	case 3:		/* Node ID */
 		node = ints[3];
+		/* Fall through */
 	case 2:		/* IRQ */
 		irq = ints[2];
+		/* Fall through */
 	case 1:		/* IO address */
 		io = ints[1];
 	}