drm/fsl-dcu: Fix return type of fsldcudrmconnectormode_valid()
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 43a0bc53b767405a8ba137d996609c6a9e36a0f4. For more details please see the references link.