MAINTAINERS: remove Thomas Falcon from IBM ibmvnic

MAINTAINERS: remove Thomas Falcon from IBM ibmvnic

We have not seen emails or tags from Thomas's IBM address
(tlfalcon@linux.ibm.com) in over 5 years. Looks like Thomas
is active in perf tooling at Intel (thomas.falcon@intel.com).

Subsystem IBM Power SRIOV Virtual NIC Device Driver
  Changes 49 / 134 (36%)
  Last activity: 2025-08-26
  Haren Myneni <haren@linux.ibm.com>:
    Tags 3c14917953a5 2025-08-26 00:00:00 2
  Rick Lindsley <ricklind@linux.ibm.com>:
  Nick Child <nnac123@linux.ibm.com>:
    Author d93a6caab5d7 2025-03-25 00:00:00 14
    Tags d93a6caab5d7 2025-03-25 00:00:00 16
  Thomas Falcon <tlfalcon@linux.ibm.com>:
  Top reviewers:
    [22]: drt@linux.ibm.com
    [13]: horms@kernel.org
    [9]: ricklind@linux.vnet.ibm.com
    [3]: davemarq@linux.ibm.com
  INACTIVE MAINTAINER Thomas Falcon <tlfalcon@linux.ibm.com>

Move Thomas to CREDITS as the initial author of ibmvnic.

Acked-by: Thomas Falcon <thomas.falcon@intel.com>
Link: https://patch.msgid.link/20260303215339.2333548-12-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>