dsp: Add check for negative value size

There is a possibility where an access
to /dev/msm_audio_cal from third party
could pass negative size which would
lead to crash.
Avoid this by negative value size check.

Change-Id: Id36c5f10dccbd7d0ee85aa3310badec6815237a2
Signed-off-by: Sujin Panicker <quic_spanic@quicinc.com>