Unimplemented clock operations should be simply omitted instead of returning
error values.

This patch removes unimplemented PLL operations to fix problems caused
by returning error code in round_rate callback.
Signed-off-by: NTomasz Figa <t.figa@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: NThomas Abraham <thomas.abraham@linaro.org>
Acked-by: NMike Turquette <mturquette@linaro.org>
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>