MAINTAINERS: adjust to filesystem doc ReST conversion

MAINTAINERS: adjust to filesystem doc ReST conversion

Mauro's patch series <cover.1581955849.git.mchehab+huawei@kernel.org>
("[PATCH 00/44] Manually convert filesystem FS documents to ReST")
converts many Documentation/filesystems/ files to ReST.

Since then, ./scripts/get_maintainer.pl --self-test complains with 27
warnings on Documentation/filesystems/ of this kind:

  warning: no file matches F: Documentation/filesystems/...

Adjust MAINTAINERS entries to all files converted from .txt to .rst in the
patch series and address the 27 warnings.

Link: https://lore.kernel.org/linux-erofs/cover.1581955849.git.mchehab+huawei@kernel.org
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20200314175030.10436-1-lukas.bulwahn@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>