dsp: voice: Remove common lock before sending unmap command

Remove common mutex lock before invoking unmap physical
memory command to avoid deadlock issue between voice lock
and common lock in concurrency use cases.

Change-Id: Iaca089f4ff1b6da16e0e59939088fb59516362aa
Signed-off-by: Aditya Bavanari <abavanar@codeaurora.org>