media: tc358746: Move clk_prepare to its own function

Smatch is very confused by a clk_prepare_enable() being called in an
error-path. Fix this warning by moving the clk_prepare_enable() to its
own function.

drivers/media/i2c/tc358746.c:1631 tc358746_suspend() warn: 'tc358746->refclk' from clk_prepare_enable() not released on lines: 1631.

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>