[media] soc-camera: use devm_kzalloc in subdevice drivers

I2C drivers can use devm_kzalloc() too in their .probe() methods. Doing so
simplifies their clean up paths.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>