media: sun6i-csi: Always set exclusive module clock rate

In some situations the default rate of the module clock is not the
required one for operation (for example when reconfiguring the clock
tree to use a different parent). As a result, always set the correct
rate for the clock (and take care of cleanup).

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>