media: meson: vdec_1: Refactor vdec_1_stop()

Factor out all the power off logic, except the clk_disable_unprepare(),
to a new function __vdec_1_stop().

This allows vdec_1_start() to explicitly clean-out the clock during the
error-path.

The following smatch warning is fixed:
drivers/staging/media/meson/vdec/vdec_1.c:239 vdec_1_start() warn: 'core->vdec_1_clk' from clk_prepare_enable() not released on lines: 239.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>