MAINTAINERS: Add myself as a maintainer for vc4

Eric isn't working on vc4 anymore and I've been working on it, as well as
merging patches for it, recently so let's make it official so I don't miss
patches.

Signed-off-by: Maxime Ripard <[e-mail]>
Reviewed-by: Eric Anholt <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

MAINTAINERS

···
 
 DRM DRIVERS FOR VC4
 M:	Eric Anholt <[e-mail]>
+M:	Maxime Ripard <[e-mail]>
 S:	Supported
 T:	git git://github.com/anholt/linux
 T:	git git://anongit.freedesktop.org/drm/drm-misc