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.

Fixes: 16bbc3eb

 ("rsi: fix null pointer dereference during rsi_shutdown()")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230527222833.273741-1-marex@denx.de