qos: Register irq notify after adding the qos request

Before adding the irq affinity based qos request to the list, if
the affinity of the interrupt changes it will trigger notify call.
This notifier call will try to update the qos request. Accessing
the qos request which is not yet added to the list leads to a
NULL pointer exception.

Avoid this race by registering the notifier after adding the
qos request.

Change-Id: I99869cc233573b5db10e4f3224d65c29511050ea
Signed-off-by: Anil Kumar Mamidala <amami@codeaurora.org>