mailmap: add John Crispin's entry

John has not been CCed on some of the fixes which perhaps resulted
in the lack of review tags:

Subsystem MEDIATEK ETHERNET DRIVER
  Changes 50 / 295 (16%)
  Last activity: 2023-01-17
  Felix Fietkau <[email protected]>:
    Author 8bd8dcc 2022-11-18 00:00:00 33
    Tags 8bd8dcc 2022-11-18 00:00:00 38
  John Crispin <[email protected]>:
  Sean Wang <[email protected]>:
    Author 880c2d4 2019-06-03 00:00:00 7
    Tags a5d7553 2020-04-07 00:00:00 10
  Mark Lee <[email protected]>:
    Author 8d66a81 2019-11-14 00:00:00 4
    Tags 8d66a81 2019-11-14 00:00:00 4
  Lorenzo Bianconi <[email protected]>:
    Author 08a764a 2023-01-17 00:00:00 68
    Tags 08a764a 2023-01-17 00:00:00 74
  Top reviewers:
    [12]: [email protected]
    [6]: [email protected]
    [6]: [email protected]
  INACTIVE MAINTAINER John Crispin <[email protected]>

map his old address to the up to date one.

Acked-by: John Crispin <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>

.mailmap

@@ -214,6 +214,7 @@ Jisheng Zhang <[email protected]> <[email protected]>
 Jisheng Zhang <[email protected]> <[email protected]>
 Johan Hovold <[email protected]> <[email protected]>
 Johan Hovold <[email protected]> <[email protected]>
+John Crispin <[email protected]> <[email protected]>
 John Paul Adrian Glaubitz <[email protected]>
 John Stultz <[email protected]>
 Jordan Crouse <[email protected]> <[email protected]>