Revert "mt76: probe load mt7615 driver asynchronously"

Revert "mt76: probe load mt7615 driver asynchronously"

This reverts commit 81764319637f ("mt76: probe load mt7615 driver
asynchronously").  After said commit, users report that MT7615 no longer
works on boot and they have to manually enable WiFi (via command "wifi") to
make it working again.

Fixes: FS#2546
Ref: https://forum.openwrt.org/t/xiaomi-r3p-no-wifi-on-boot/45509
Signed-off-by: DENG Qingfang <dengqf6@mail2.sysu.edu.cn>
[commit description facelift]
Signed-off-by: Petr Štetiar <ynezz@true.cz>