[media] exynos4-is: Correct clock properties description at the DT binding documentation

The 'camera' DT node needs to have sclk_cam0/1 and pxl_async0/1 clocks
specified, while 'fimc' nodes should have only "fimc" and "sclk_fimc".
"mux" and "parent" are leftovers from early versions of patches adding
DT support, when the IP bus clock parent clock was being set by the
driver. A better solution is needed to have e.g. clocks driver setting
all required parent clocks, before clock consumers start using the
clocks. Currently this binding doesn't describe parent clocks setup,
it needs to be specified and handled somewhere else.

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>