mt7601u: check the status of device in calibration

When the usb device being plugged out, before ieee80211 gets to know the
hw being removed, it gets to know that the association status changed,
and thus ask for the device to do the calibration. This causes error as
the hw is absent.

This can be avoid by checking the status of the device before sending
the calibration request to the device.

Signed-off-by: Zhi Han <z.han@gmx.net>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201217161657.GB12562@E480