Fix a couple of issues with t4iov probe and attach.

• Check for Chelsio vendor ID in probe routines.
• Fail attach instead of faulting if pci_find_dbsf() doesn't find a device.

PR: 216539
Reported by: asomers
Tested by: Dave Baukus <daveb@spectralogic.com>
MFC after: 3 days
Sponsored by: Chelsio Communications