clk: samsung: Register clk provider only after registering its all clocks

Ensure the clock provider is not registered until after all its related
clocks were created and are ready to use. Currently there are races
possible and any (of_)clk_get() call right after a clock provider's
clk_init_cb callback call may fail.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Tomasz Figa <t.figa@samsung.com>