mana: fix leaking pci resource problem detaching mana deivces

Fixing the error messages when detaching the mana gdma devices
showed in dmesg: "Device leaked memory resources".

Reported by: NetApp
MFC after: 3 days
Sponsored by: Microsoft

(cherry picked from commit 47e99e5bc5bcfa621fe6a3e62386f227c47e8cff)