qcacld-3.0: mac: 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 mac replace any such comparisons with logical
operations performed on the pointer itself.

Change-Id: I387e08b1ba4d46e6b5ca5cf08ba398a32a3a00d4
CRs-Fixed: 2418392
44 files changed