M2M scaler clocks require special handling of their parent bus clock during
power domain on/off sequences. MSCL clocks were not initially added to the
sub-CMU handler, because that time there was no driver for the M2M scaler
device and it was not possible to test it.

This patch fixes this issue. Parent clock for M2M scaler devices is now
properly preserved during MSC power domain on/off sequence. This gives M2M
scaler devices proper performance: fullHD XRGB32 image 1000 rotations test
takes 3.17s instead of 45.08s.

Fixes: b06a532b ("clk: samsung: Add Exynos5 sub-CMU clock driver")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lkml.kernel.org/r/20190808121839.23892-1-m.szyprowski@samsung.comAcked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>