MAINTAINERS: repair file pattern in MEDIATEK IOMMU DRIVER

Commit 6af48738 ("MAINTAINERS: Add entry for MediaTek IOMMU") mentions
the pattern 'drivers/iommu/mtk-iommu*', but the files are actually named
with an underscore, not with a hyphen.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains:

  warning: no file matches  F:    drivers/iommu/mtk-iommu*

Repair this minor typo in the file pattern.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Yong Wu <yong.wu@mediatek.com>
Link: https://lore.kernel.org/r/20210208061025.29198-1-lukas.bulwahn@gmail.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

MAINTAINERS

@@ -11184,7 +11184,7 @@ L:	iommu@lists.linux-foundation.org
 L:	linux-mediatek@lists.infradead.org (moderated for non-subscribers)
 S:	Supported
 F:	Documentation/devicetree/bindings/iommu/mediatek*
-F:	drivers/iommu/mtk-iommu*
+F:	drivers/iommu/mtk_iommu*
 F:	include/dt-bindings/memory/mt*-port.h
 
 MEDIATEK JPEG DRIVER