crypto: msm: Fix XO shutdown issues

ce-core_src clk is being left on preventing device from going
into low power mode. Furthere more, clks are enabled without
checking if the handle is valid.
This fix removes enabling of ce_crore_src_clk. Also checks if
clk handle is valid before enabling them.

Change-Id: Ieb64b4b11385838ba18dd05d47ccc978e5b1bdf1
Signed-off-by: Mona Hossain <mhossain@codeaurora.org>