clk: at91: Fix at91-pmc and at91-sckc's class ID

clk: at91: Fix at91-pmc and at91-sckc's class ID

The at91-pmc and at91-sckc aren't the clock providers, change their
class ID from UCLASS_CLK to UCLASS_SIMPLE_BUS, they also don't
need to bind the child nodes explicitly, the .post_bind callback
of simple_bus uclass will do it for them.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>