MAINTAINERS: Add Jianjun Wang as MediaTek PCI co-maintainer

Update entry for MediaTek PCIe controller, add Jianjun Wang
as MediaTek PCI co-maintainer.

Link: https://lore.kernel.org/r/20210420061723.989-8-jianjun.wang@mediatek.com


Signed-off-by: Jianjun Wang <jianjun.wang@mediatek.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Ryder Lee <ryder.lee@mediatek.com>