clk: samsung: Use clk_hw API for calling clk framework from clk notifiers

clk_notifier_register() documentation states, that the provided notifier
callbacks associated with the notifier must not re-enter into the clk
framework by calling any top-level clk APIs. Fix this by replacing
clk_get_rate() calls with clk_hw_get_rate(), which is safe in this
context.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <snawrocki@kernel.org>