ath10k: unregister spectral before mac

If spectral is unregistered after mac80211, the relayfs file has already
been removed recursively by mac/cfg80211, and spectral tries to remove
the file once more, thus leading to double free problems. Better clean
up spectral before to avoid that problem.

Reported-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>