power: qpnp-bms: initialize mutexes earlier

The mutex "bms_output_lock" can be used in the
read_iadc_channel_select function of the bms driver's probe routine.
However, at this time the mutex is not initialized, and can cause a
crash. Fix this by initializing the bms driver mutexes earlier in the
probe routine.

CRs-Fixed: 510669
Change-Id: Ic57adce617a1354d7b96e3e710cfa7e534135622
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>