clk: qcom: Remove mux flag

If a mux has on/off capability, always write to the en_offset register
instead of optionally writing to the offset register if a flag is set.
This reduces code complexity.

Change-Id: Ia0ea975403407c716131679d2e94e5bf33b85749
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>