wlan: De-register interrupts while doing SSR

While doing SSR, Tx and Rx interrupts can trigger
before shutdown completes, this can cause interrupts
trigger during shutdown process.

To address this de-register Tx and Rx interrupts
immediately when shutdown is triggered.

Change-Id: I8abe625048f80e47cbd217a7c0cb3205a2a6a042
CRs-Fixed: 2748613