ASoC: msm: avoid negative time stamp check

Time stamp is unsigned. There is no need to check for
negative value.

Change-Id: I15e380f81e46908f6a9fe8d29c174de1b7c33173
CRs-fixed: 423372
Signed-off-by: Patrick Lai <plai@codeaurora.org>

Conflicts:
	arch/arm/mach-msm/qdsp6v2/audio_lpa.c
	include/sound/q6asm-v2.h
	sound/soc/msm/qdsp6v2/msm-compr-q6-v2.c
	sound/soc/msm/qdsp6v2/msm-pcm-lpa-v2.c
	sound/soc/msm/qdsp6v2/q6asm.c