drm/mediatek: Add 0 size check to mtk_drm_gem_obj

In the Linux kernel, the following vulnerability has been resolved:

drm/mediatek: Add 0 size check to mtk_drm_gem_obj

Add a check to mtk_drm_gem_init if we attempt to allocate a GEM object

of 0 bytes. Currently, no such check exists and the kernel will panic if

a userspace application attempts to allocate a 0x0 GBM buffer.

Tested by attempting to allocate a 0x0 GBM buffer on an MT8188 and

verifying that we now return EINVAL.