[media] s5p-mfc: Remove special clock usage in driver

MFC uses two clocks - MFC gate clock and special clock
which is named as "sclk_mfc" in exynos4 and "aclk_333" in
exynos5 SoC. The driver was doing just a clk_prepare on
this special clock without a clk_enable call. As this
sclk is the parent of gate clock, it gets prepared and
enabled along with the gate clock. So there is no need
for the driver to use this sclk. This patch removes the
sclk usage from driver.

Signed-off-by: Arun Kumar K <arun.kk@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>