qcacmn: hif: Replace explicit comparison to NULL

Per the Linux Kernel coding style, as enforced by the kernel
checkpatch script, pointers should not be explicitly compared to
NULL. Therefore within hif replace any such comparisons with logical
operations performed on the pointer itself.

Change-Id: I929cb64ee0523d11bc86d5145aade1ec5a713071
CRs-Fixed: 2418257
23 files changed