MAINTAINERS: Remove Donald Robson from powervr driver maintainers

I will be leaving Imagination Technologies on 2023-12-15 and will no
longer be working on this driver.
Signed-off-by: Donald Robson <donald.robson@imgtec.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231214103353.122257-1-donald.robson@imgtec.com

MAINTAINERS

@@ -10407,7 +10407,6 @@ F:	drivers/media/rc/img-ir/
 
 IMGTEC POWERVR DRM DRIVER
 M:	Frank Binns <frank.binns@imgtec.com>
-M:	Donald Robson <donald.robson@imgtec.com>
 M:	Matt Coster <matt.coster@imgtec.com>
 S:	Supported
 T:	git git://anongit.freedesktop.org/drm/drm-misc