msm: npu: Avoid accessing NPU resources when it's disabled

Interrupt handler may access NPU resources when NPU is disabled
if the previous IPC command was interrupted by system signal.
This change is to fix this issue.

Change-Id: Ib0a9f8b97ac82e688a74b662715fd195b4a82039
Signed-off-by: Jilai Wang <jilaiw@codeaurora.org>