Revert "rtac: Reduce RTAC buffer size"

This reverts commit 9e16937a.

-Retain max buffer size in driver, it is userspace which
defines payload length size which gets passed to dsp.

Change-Id: I65982f6ee45ce1e021cdc0f6fe035435be3d208e
Signed-off-by: Sachin Mohan Gadag <sgadag@codeaurora.org>