Fixed using myoptarg instead of optarg

Co-Authored-By: BazookaJoe1900 <BazookaJoe1900@gmail.com>

src/drivers/magnetometer/lsm303agr/lsm303agr_main.cpp

@@ -146,7 +146,7 @@ lsm303agr_main(int argc, char *argv[])
 	while ((ch = px4_getopt(argc, argv, "XR:a:", &myoptind, &myoptarg)) != EOF) {
 		switch (ch) {
 		case 'R':
-			rotation = (enum Rotation)atoi(optarg);
+			rotation = (enum Rotation)atoi(myoptarg);
 			break;
 
 		default: