drm/mediatek: fix mtk_hdmi_setup_vendor_specific_infoframe mistake

mtk_hdmi_setup_vendor_specific_infoframe will return before handle
mtk_hdmi_hw_send_info_frame.Because hdmi_vendor_infoframe_pack
returns the number of bytes packed into the binary buffer or
a negative error code on failure.
So correct it.

Fixes: 8f83f268 ("drm/mediatek: Add HDMI support")
Signed-off-by: Nickey Yang <nickey.yang@rock-chips.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>