tools: dumpimage: Fall-though to print usage for help command

This has the same result but some compilers will warn about this
fall-through if there are statements as part of the label block.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>

tools/dumpimage.c

@@ -104,7 +104,6 @@ int main(int argc, char **argv)
 			printf("dumpimage version %s\n", PLAIN_VERSION);
 			exit(EXIT_SUCCESS);
 		case 'h':
-			usage();
 		default:
 			usage();
 			break;