[media] pxa_camera: Fix a call with an uninitialized device pointer

In 'commit 295ab497 ("[media] media: platform: pxa_camera: make
printk consistent")' a pointer to the device structure in
mclk_get_divisor() was changed to pcdev_to_dev(pcdev). The pointer used
by pcdev_to_dev() is still uninitialized during the call to
mclk_get_divisor() as it happens in v4l2_device_register() at the end
of the probe. The dev_warn and dev_dbg caused a line in the log:

	(NULL device *): Limiting master clock to 26000000

Fix this by using an initialized pointer from the platform_device
(as before the old patch).

Signed-off-by: Petr Cvek <petr.cvek@tul.cz>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>