MAINTAINERS: Remove unneded wildcard for the i915 DRM driver

There is no other file but the UAPI header, thus we can drop the
wildcard.

Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1461279842-28695-3-git-send-email-emil.l.velikov@gmail.com