[media] s5p-fimc: Add clk_prepare/unprepare for sclk_cam clocks

Add clk_prepare(), clk_unprepare() calls for the sclk_cam clocks
to ensure the driver works on platforms with the common clocks
API enabled.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>