ASoC: wcd9335: reset CPE TX PP buffer memory

From second detection onwards, buffered data has one extra
stale sample before the actual data even though CPE TX PP
(PingPong) buffer is properly disabled. Avoid this extra data
by clearing TX PP buffer memory after reading the complete buffer.

Change-Id: Id3183f64136e827641ab4d00450dbdb7806f00ab
Signed-off-by: Vidyakumar Athota <vathota@codeaurora.org>