USB: msm: Use new clock framework APIs

Clock framework now provides two new APIs: clk_prepare and
clk_unprepare which can be called from non-atomic context only.
Other clk_enable and clk_disable APIs can be called from atomic
context.
To enable a clock drivers need to call both clk_prepare and
clk_enable. Similarly for disabling a clock - clk_disable and
clk_unprepare should be called.

Change-Id: I1ec0764e34619b92d811e1dadd2bb49b5cf36f5c
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>