drm/mediatek: Fix return type of mtkhdmibridgemodevalid()
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v6.0.16 by commit cb5b1d1c979d502e454f40dee10e90242edc0300. For more details please see the references link.