[nrf fromtree] drivers: nrfx: Avoid unhandled event calling assert function

Avoid unhandled event calling assert function

Signed-off-by: Matthias Hauser <[email protected]>
(cherry picked from commit 5438643)

Author: mah-eiSmart

drivers/clock_control/clock_control_nrf.c

@@ -637,6 +637,11 @@ static void clock_event_handler(nrfx_clock_evt_type_t event)
 			__ASSERT_NO_MSG(false);
 		}
 		break;
+	case NRFX_CLOCK_EVT_PLL_STARTED:
+	{
+		/* unhandled event */
+		break;
+	}
 	default:
 		__ASSERT_NO_MSG(0);
 		break;