hosted/cli: Fix minor implicit fallthrough

* CMSIS-DAP and GPIOD backends are runtime mutually exclusive, but
  GCC still rightfully prints a diagnostic
* Terminate every case with a break.

src/platforms/hosted/cli.c

@@ -421,6 +421,7 @@ void cl_init(bmda_cli_options_s *opt, int argc, char **argv)
 		case 'g':
 			if (optarg)
 				opt->opt_gpio_map = optarg;
+			break;
 #endif
 		case 'k':
 			opt->opt_cmsisdap_allow_fallback = true;