hwc2: Ignore Notify to non-existance file node

Secure display will try to signal both wled and labibb. However
the display function did not use WLED to drive backlight, nor use
LAB/IBB of the PMIC to provide the LCD bias on B4S4.
So just bypass the file node writing if it's invalid.

Bug: 111504659
Test: Manually tested with keystore_cli_v2

Change-Id: Ia7ea7c13a7635a7f81ae6d76dd1627791c7e49bf
1 file changed