byte-cntr: Add init_completion for small data transfer

Add Add init_completion for small data transfer case to avoid issue
when call wait_for_completion in qdss_close.

Change-Id: I15e4d98def1e21c85fbb15780671ddeea3db79b7
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>