powerpc/8xx: Update email address in MAINTAINERS

Since 01 May 2020, our email adresses have changed to @csgroup.eu

Update MAINTAINERS accordingly.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9fd0f9a827ebbeae64ad7a6f6c595d242f4dd5fc.1588747860.git.christophe.leroy@csgroup.eu

MAINTAINERS

@@ -9786,7 +9786,7 @@ F:	arch/powerpc/platforms/83xx/
 F:	arch/powerpc/platforms/85xx/
 
 LINUX FOR POWERPC EMBEDDED PPC8XX
-M:	Christophe Leroy <christophe.leroy@c-s.fr>
+M:	Christophe Leroy <christophe.leroy@csgroup.eu>
 L:	linuxppc-dev@lists.ozlabs.org
 S:	Maintained
 F:	arch/powerpc/platforms/8xx/