Linux: I2C opens /dev/i2c-x

For now it uses the bus number as the id. Not sure how this should
actually be mapped.

Seems like the I2C devices come up in random order and have random
id but that a specific device can be found in the /sys/bus/i2c
interface.

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

src/drivers/blinkm/blinkm_linux.cpp

@@ -943,6 +943,10 @@ blinkm_main(int argc, char *argv[])
 
 	int x;
 
+	if (argc < 2) {
+		blinkm_usage();
+		return 1;
+	}
 	for (x = 1; x < argc; x++) {
 		if (strcmp(argv[x], "-b") == 0 || strcmp(argv[x], "--bus") == 0) {
 			if (argc > x + 1) {