rtac: Reduce RTAC buffer size

Currently RTAC buffer size is 163k which is uint32_t max, but
dsp expects buffer size of max of uint16_t for get_param_data_V5 api.
Hence reduce size to 57344 which is highest unsigned 2byte (0xE000)
integer and multiple of 8192.

Change-Id: I7e866a537fd39ffd43eb4e4e6b82e3d4dffad74d
Signed-off-by: Sachin Mohan Gadag <sgadag@codeaurora.org>