ath10k: don't enable interrupts for the diagnostic window

The diagnostic window (CE7) uses polling and is not initiliased to retrieve
interrupts so disable interrupts altogether for CE7. Otherwise ath10k crashes
when using the diagnostic window while the firmware is running due to NULL
dereference and polling reads timeout.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>