cxgbe/cxgbei: Do not validate the hardware iSCSI tag mask.

This was added in 7cba15b16eb2 in 2016 and firmwares at that time were
already setting up the iSCSI tag mask properly. Since then it has also
become possible to split the iSCSI region between multiple PCIE PFs but
the driver's calculation takes only its own PF's allocation into account
and that means this code is incorrect and not just a harmless no-op.

MFC after: 1 week
Sponsored by: Chelsio Communications