MAINTAINERS: Update drm-misc.git URL

Now that the drm-misc tree has moved to Gitlab, adjust the MAINTAINERS
git trees to reflect the location change.

Link: https://lore.kernel.org/r/20240306153841.698693-1-mripard@kernel.orgAcked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Maxime Ripard <mripard@kernel.org>