cosmetic: osmo-sim-test.c: use memcpy instead of strncpy

gcc 8.1.0 complains that the terminating \0 is not copied by strncpy, while
this code intends to do exactly that. Use memcpy instead.

Change-Id: I8d66fa22502c04d11ae153b9856d7e54f3492dd6
diff --git a/utils/osmo-sim-test.c b/utils/osmo-sim-test.c
index ea24120..5588294 100644
--- a/utils/osmo-sim-test.c
+++ b/utils/osmo-sim-test.c
@@ -74,7 +74,8 @@
 	msg = osim_new_apdumsg(0x00, 0x20, 0x00, pin_nr, 8, 0);
 	pindst = (char *) msgb_put(msg, 8);
 	memset(pindst, 0xFF, 8);
-	strncpy(pindst, pin, strlen(pin));
+	/* Do not copy the terminating \0 */
+	memcpy(pindst, pin, strlen(pin));
 
 	return osim_transceive_apdu(st, msg);
 }