When audio sample rate which set to audio track is not the same with
the actual pcm data, noise will be heard. Fix the bug when write 8 bit
pcm samples.
Change-Id: Idcb0d7b0e9aaa250dd22b758c8337e23d1706049 Signed-off-by: Ming Zhou <b42586@freescale.com> Signed-off-by: guoyin.chen <guoyin.chen@freescale.com>