cpufreq: Fix fall-through warning for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a
fallthrough warning by simply dropping the empty default case at
the bottom.

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <[e-mail]>

drivers/cpufreq/longhaul.c

···
 		return cpufreq_register_driver(&longhaul_driver);
 	case 10:
 		pr_err("Use acpi-cpufreq driver for VIA C7\n");
-	default:
-		;
 	}
 
 	return -ENODEV;