MAINTAINERS: change mediatek wiki page

The old wiki page unfortunately got lost by server crash.
The new wiki can be found on the kernel.org infrastructure
Signed-off-by: NMatthias Brugger <matthias.bgg@gmail.com>
Reviewed-by: NChun-Kuang Hu <chunkuang.hu@kernel.org>
Link: https://lore.kernel.org/r/20201020152639.21950-1-matthias.bgg@kernel.orgSigned-off-by: NMatthias Brugger <matthias.bgg@gmail.com>

MAINTAINERS

@@ -2067,7 +2067,7 @@ M:	Matthias Brugger <matthias.bgg@gmail.com>
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 L:	linux-mediatek@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained
-W:	https://mtk.bcnfs.org/
+W:	https://mtk.wiki.kernel.org/
 C:	irc://chat.freenode.net/linux-mediatek
 F:	arch/arm/boot/dts/mt6*
 F:	arch/arm/boot/dts/mt7*