[media] exynos4-is: Remove "sysreg" clock handling

The "sysreg" clock is required by multiple subsystems and none of the
other drivers handles this clock explicitly. It is currently assumed
that this clock is always on, left in its default state after system
reset.
Remove handling of this clock from the FIMC-IS driver to avoid breaking
other subsystems.

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>