qtnfmac: do not use mutexes in timer context

The function qtnf_scan_done makes use of mutexes which is wrong
since it may be called from timer context. Move scan timeout
handler from timer to deferred work.

Signed-off-by: Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>