MAINTAINERS: downgrade myself to Reviewer for s390

Now that Alexander Gordeev has volunteered to be a co-maintainer for
s390, I can act as a reviewer instead of being a maintainer for s390.
With Alexander, Heiko, and Vasily we are in really good shape.
I will continue to act as the maintainer for KVM on s390 together with
Janosch.

Signed-off-by: Christian Borntraeger <[email protected]>
Acked-by: Heiko Carstens <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>

Author: borntraeger

MAINTAINERS

@@ -16817,8 +16817,8 @@ F:	drivers/video/fbdev/savage/
 S390
 M:	Heiko Carstens <[email protected]>
 M:	Vasily Gorbik <[email protected]>
-M:	Christian Borntraeger <[email protected]>
 M:	Alexander Gordeev <[email protected]>
+R:	Christian Borntraeger <[email protected]>
 R:	Sven Schnelle <[email protected]>
 L:	[email protected]
 S:	Supported