wifi: rtw88: Use rtw_iterate_vifs() for rtw_vif_watch_dog_iter()

USB and (upcoming) SDIO support may sleep in the read/write handlers.
Make rtw_watch_dog_work() use rtw_iterate_vifs() to prevent "scheduling
while atomic" or "Voluntary context switch within RCU read-side
critical section!" warnings when accessing the registers using an SDIO
card (which is where this issue has been spotted in the real world but
it also affects USB cards).

Fixes: 78d5bf92 ("wifi: rtw88: iterate over vif/sta list non-atomically")
Suggested-by: Ping-Ke Shih <pkshih@realtek.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Tested-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230108211324.442823-3-martin.blumenstingl@googlemail.com