media: mediatek: vpu: add missing clk_unprepare

If vpu_clock_enable() fails, then call clk_unprepare().

This fixes this smatch warning:

drivers/media/platform/mediatek/vpu/mtk_vpu.c:1031 mtk_vpu_resume() warn: 'vpu->clk' from clk_prepare() not released on lines: 1020.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Yunfei Dong <yunfei.dong@mediatek.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>