wcn36xx: Run suspend for the first ieee80211_vif

A subsequent set of patches will extend out suspend/resume support in this
driver, we cannot set the firmware up for multiple ipv4/ipv6 addresses and
as such we can't iterate through a list of ieee80211_vif.

Constrain the interaction with the firmware to the first ieee80211_vif on
the suspend/resume/wowlan path.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Tested-by: Benjamin Li <benl@squareup.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210605011140.2004643-3-bryan.odonoghue@linaro.org