drivers: display: st7789v: remove incorrect error check

The st7789v_transmit function does not return any error code (void), so
ret = st7789v_transmit(...) is wrong.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

Author: gmarull

drivers/display/display_st7789v.c

@@ -407,7 +407,7 @@ static int st7789v_pm_control(const struct device *dev,
 		st7789v_exit_sleep(data);
 		break;
 	case PM_DEVICE_ACTION_SUSPEND:
-		ret = st7789v_transmit(data, ST7789V_CMD_SLEEP_IN, NULL, 0);
+		st7789v_transmit(data, ST7789V_CMD_SLEEP_IN, NULL, 0);
 		break;
 	default:
 		ret = -ENOTSUP;