qcom: smb2: ensure QC adapter is at 5V at shutdown

In the shutdown hook, driver forces adapter to 5V but
there is a possibility that the source change IRQ triggers
and moves back the adapter to 9V.
To avoid this and any race between the irq's and shutdown path,
disable all irqs as the first step in shutdown path.

CRs-Fixed: 2032575
Change-Id: I0d8f59a73b6631e9bf6f5d64dd215c239e7772fe
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>