soc: qcom: bam_dmux: Use memset()

Bam_dmux needs to zero out a pair of buffers as part of the BAM reset
proceedure.  __memzero() is a convenient mechanism to accomplish this, but
it is not always available.

Replace __memzero() usage with memset() as memset() is always available.

Change-Id: I9e83335ee8e838af405b6f8e8b772db68560f4ef
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>