MAINTAINERS: drm: fsl-dcu: Update to Alison's NXP email address

The freescale.com email domain is not valid anymore, so use
the nxp.com domain instead.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>