dey-examples: adc: fix help output

When not enough arguments are given (this includes using only the '-h'
argument for help), show the complete help.

Signed-off-by: Diaz de Grenu, Jose <Jose.DiazdeGrenu@digi.com>

meta-digi-dey/recipes-digi/dey-examples/files/adc_sample/adc_sample.c

@@ -196,7 +196,7 @@ int main(int argc, char **argv)
 	int ret, opt, i;
 
 	if (argc <= 2) {
-		show_usage(0);
+		show_usage(1);
 		return EXIT_FAILURE;
 	}