[media] soc_camera: Don't call .s_power() during probe

The .s_power() call only covers the .g_mbus_fmt() operation call.
Several clients required to be powered on to retrieve the current mbus
format but have now been fixed. The .s_power() call is thus not needed
anymore and can be removed.

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