clk: qcom: Move prepare_enable of XO clock before spinlock

clk_prepare would hold a mutex and as clk_debug_mux_measure_rate has
already acquired a spinlock it would result in a BUG from sleeping context.
Avoid this by moving the prepare_enable before acquiring spinlock.

Change-Id: Ia405c884663ef80e87ae066df09f1c30134faf2e
Signed-off-by: Taniya Das <tdas@codeaurora.org>