Fixed usage string for hello app

hello should have been hello_main

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/platforms/linux/hello/hello_start_linux.cpp

@@ -95,6 +95,6 @@ int hello_main(int argc, char *argv[])
 		return 0;
 	}
 
-	printf("usage: hello {start|stop|status}\n");
+	printf("usage: hello_main {start|stop|status}\n");
 	return 1;
 }