wcn36xx: Change indication list lock to spinlock

In preparation for handling incoming messages from IRQ context, change
the indication list lock to a spinlock

Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>