ASoC: msm8930: properly protect external mclk control function

Both audio path and MBHC accessory detection logic need master clock
enabled along with bandgap and clock block of CODEC. Clock control
is managed by the machine driver. Calls to clock control function from
audio and MBHC detection paths can be nested. As a result, reference
counter of master clock is incremen/decrement out of order and cause
master clock not enabled when audio path is enabled. Without master clock
CODEC will not consume data and this leads to SLIMBUS overflow error.

CRs-Fixed: 469683
Change-Id: Ib3a55f5d0b36ebe9ba345e7f18162a9314500df2
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>