wcnss: add null check in pm_ops unregister

Add null check for pm_ops in pm_ops unregister to avoid
null pointer dereference.

Change-Id: I885618a3244b91ba5eddcadb81ae08e965db63b3
CRs-Fixed: 690191
Signed-off-by: Mahesh A Saptasagar <msapta@codeaurora.org>
Merge "wcnss: add null check in pm_ops unregister"
Merge ec8ceb10a807d171ad67e543aeb9fc9b00bb2887 on remote branch

Change-Id: Ie0d30dac8bb060fc9d1c3f42a8f21c23b2671a4f
Merge "Merge ec8ceb10a807d171ad67e543aeb9fc9b00bb2887 on remote branch"