wifi: mt76: mt792x: fix scheduler interference in drv own process

Add some time to wait for LP engine to complete its operation
before polling pmctrl register.

Signed-off-by: Michael Lo <michael.lo@mediatek.com>
Signed-off-by: Ming Yen Hsieh <mingyen.hsieh@mediatek.com>
Tested-by: David Ruth <druth@chromium.org>
Acked-by: Sean Wang <sean.wang@mediatek.com>
Link: https://patch.msgid.link/20240523112131.31437-1-mingyen.hsieh@mediatek.com


Signed-off-by: Felix Fietkau <nbd@nbd.name>