qcacmn: Avoid NULL pointer dereference of pointer 'pPacket'

Pointer 'pPacket' returned from call to the function
'htc_packet_dequeue' may be NULL.

Add a NULL check for pPacket before dereferencing it.

Change-Id: I1ecb82cce0fc00877b3ec2de2676027dde261186
CRs-Fixed: 2478206