ASoC: msm-pcm-voip: Avoid interger underflow

There is no check for voip pkt pkt_len,if it contains the
min required data. This can lead to integer underflow.
Add check for the same.

Change-Id: I40242429542b6c32a0e6c3bbe03975c244c2f61a
Signed-off-by: Soumya Managoli <quic_c_smanag@quicinc.com>