MAINTAINERS: Add myself as maintainer for arch/sh (SUPERH)

Both Rich Felker and Yoshinori Sato haven't done any work on arch/sh
for a while. As I have been maintaining Debian's sh4 port since 2014,
I am interested to keep the architecture alive.
Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Acked-by: Yoshinori Sato <ysato@users.sourceforge.jp>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -20090,6 +20090,7 @@ F:	drivers/watchdog/sunplus_wdt.c
 SUPERH
 M:	Yoshinori Sato <ysato@users.sourceforge.jp>
 M:	Rich Felker <dalias@libc.org>
+M:	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
 L:	linux-sh@vger.kernel.org
 S:	Maintained
 Q:	http://patchwork.kernel.org/project/linux-sh/list/