devices: fix 'NotImplemented' usage
devices: fix 'NotImplemented' usage

'__eq__' function should return 'NotImplemented' _value_, not
'NotImplementedError' exception.

marmarek/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin