drm/sti: Fix return type of sti_{dvo,hda,hdmi}connectormode_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 v4.9.337 by commit b2c92b2a3801b09b709cbefd9a9e4944b72400bf. For more details please see the references link.