clk: ccf: correct the test on the parent uclass in clk_enable/clk_disable

It is safe to check if the uclass id on the device is UCLASS_CLK
before to call the clk_ functions, but today this comparison is
not done on the device used in API: clkp->dev->parent
but on the device himself: clkp->dev.

This patch corrects this behavior and tests if the parent device
is a clock device before to call the clock API, clk_enable or
clk_disable, on this device.

Fixes: 0520be0f ("clk: prograte clk enable/disable to parent")
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>