I changed the file according to your recommendation. I still get the same error:
=> Adding device-tree overlay 'verdin-imx8mp_backlight_overlay.dts'
Error: verdin-imx8mp_backlight_overlay.dts:7.13-14 syntax error
FATAL ERROR: Unable to parse input tree
error: cannot apply verdin-imx8mp_backlight_overlay.dts.