media: pxa_camera: Drop the v4l2-clk clock register

Now that mach-based PXA platforms are registering proper
fixed-rate clocks through the CCF, the v4l2-clk clock
is no longer required.

Drop this clock, so the driver no longer depends on the
legacy v4l2-clk API.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Acked-by: Petr Cvek <petrcvekcz@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>