driver: Don't initialize brightness in get_brightness()

https://lore.kernel.org/dri-devel/[email protected]/
> No need to read the brightness here. It will be set if
> mipi_dsi_dcs_get_display_brightness() succeeds.

Author: stephan-gh

driver.py

@@ -295,7 +295,7 @@ def generate_backlight(p: Panel, options: Options) -> str:
 static int {p.short_id}_bl_get_brightness(struct backlight_device *bl)
 {{
 	struct mipi_dsi_device *dsi = bl_get_data(bl);
-	u16 brightness = bl->props.brightness;
+	u16 brightness;
 	int ret;
 
 	dsi->mode_flags &= ~MIPI_DSI_MODE_LPM;