drm/fsl-dcu updates

- Update MAINTAINERS file to reflect correct email address
Signed-off-by: Dave Airlie <airlied@redhat.com>

# gpg: Signature made Mon 21 May 2018 05:52:58 AEST
# gpg:                using RSA key 4FC170DF4AEFC52F
# gpg: Can't check signature: public key not found
Link: https://patchwork.freedesktop.org/patch/msgid/20180520220238.5187-1-stefan@agner.ch