mailmap: Fix broken author information for Evan Couzens

Once again, broken commits have been merged with incorrect author
information. Fix this in .mailmap.

Before this patch (git shortlog):

viggo.jf.intel.com (2):
      doc: Move code contribution info to wiki.
      doc: Move code conventions to Zephyr wiki.

After the patch:

Evan Couzens (2):
      doc: Move code contribution info to wiki.
      doc: Move code conventions to Zephyr wiki.

Change-Id: I382c06b49fdc5f6c81bc9ec952c5958b4e1ca144
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>