wl3501_cs: Add spinlock to wl3501_reset

Likely wl3501_reset should acquire spinlock as wl3501_{open, close}.
One of calls of wl3501_reset has been already protected.
The others were unprotected and might lead to a race condition.
The patch adds spinlock into the wl3501_reset and removes it from
wl3501_tx_timeout.

Found by Linux Driver Verification project (linuxtesting.org)

Signed-off-by: Pavel Andrianov <andrianov@ispras.ru>
Acked-by: Vaishali Thakkar <vaishali.thakkar@oracle.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>