msm: ipa: freeing null pointer causing device crash

Adding check to verify the pointer null or not
before freeing the pointer.

Change-Id: Id6fd3d1d099ed545083338192d644790574b1a9c
Acked-by: Ashok Vuyyuru <avuyyuru@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>