media: meson: vdec: add missing clk_disable_unprepare on error in vdec_hevc_start()

Add the missing clk_disable_unprepare() before return
from vdec_hevc_start() in the error handling case.

Fixes: 823a7300 (“media: meson: vdec: add common HEVC decoder support”)
Signed-off-by: Xu Qiang <xuqiang36@huawei.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>