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.

Fixes: 119f5173 ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")
Signed-off-by: Justin Green <greenjustin@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240307180051.4104425-1-greenjustin@chromium.org/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>