arcnet: com90io: Mark expected switch fall-throughs

Mark switch cases where we are expecting to fall through.

This patch fixes the following warnings (Building: powerpc allyesconfig):

drivers/net/arcnet/com90io.c: In function 'com90io_setup':
include/linux/printk.h:304:2: warning: this statement may fall through [-Wimplicit-fallthrough=]
printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/arcnet/com90io.c:365:3: note: in expansion of macro 'pr_err'
pr_err("Too many arguments\n");
^~~~~~
drivers/net/arcnet/com90io.c:366:2: note: here
case 2: /* IRQ */
^~~~
drivers/net/arcnet/com90io.c:367:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
irq = ints[2];
~~~~^~~~~~~~~
drivers/net/arcnet/com90io.c:368:2: note: here
case 1: /* IO address */
^~~~

Reported-by: Stephen Rothwell <[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/com90io.c

···
 	switch (ints[0]) {
 	default:		/* ERROR */
 		pr_err("Too many arguments\n");
+		/* Fall through */
 	case 2:		/* IRQ */
 		irq = ints[2];
+		/* Fall through */
 	case 1:		/* IO address */
 		io = ints[1];
 	}