wifi: rsi: Do not configure WoWlan in shutdown hook if not enabled

In the Linux kernel, the following vulnerability has been resolved:

wifi: rsi: Do not configure WoWlan in shutdown hook if not enabled

In case WoWlan was never configured during the operation of the system,

the hw->wiphy->wowlan_config will be NULL. rsi_config_wowlan() checks

whether wowlan_config is non-NULL and if it is not, then WARNs about it.

The warning is valid, as during normal operation the rsi_config_wowlan()

should only ever be called with non-NULL wowlan_config. In shutdown this

rsi_config_wowlan() should only ever be called if WoWlan was configured

before by the user.

Add checks for non-NULL wowlan_config into the shutdown hook. While at it,

check whether the wiphy is also non-NULL before accessing wowlan_config .

Drop the single-use wowlan_config variable, just inline it into function

call.