qcacld-3.0: Validate hdd ctx
Use of wlan_hdd_validate_context is returning failure when driver load/unload
is in progress. Instead of using wlan_hdd_validate_context, we can check for
NULL pointer to validate hdd ctx in tdls disconnection callback.
Change-Id: I650aa1d4c81d5c275bb3d4266b9365b595cf0ad5
CRs-Fixed: 2036314