ASoC: msm: Fix for USB device switch

Add mutex locks to prevent sending multiple mem map
commands unless the previous one returns, because otherwise
the mem_handle is overwritten.

CRs-fixed: 646752
Change-Id: I2a472430d4505c9f74ed033260e1e99cb787e03a
Signed-off-by: Vicky Sehrawat <vickys@codeaurora.org>