drm/mgag200: Index 24 in extended CRTC registers is 24 in hex, not decimal.

This change properly enables the "requester" in G200ER cards that is
responsible for getting pixels out of memory and clocking them out to
the screen.

Signed-off-by: Christopher Harvey <charvey@matrox.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>