slim_msm: Use new clock APIs

Slimbus MSM controller driver calls clk_enable and clk_disable from
non-atomic contexts.
So the calls are just replaced by clk_prepare_enable and
clk_disable_unprepare respectively.

Change-Id: Ieaa5b62d58c153ac70c5d221888860231fedcf4e
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>