MAINTAINERS: Replace one of the maintainers for s390/pci

Add myself as co-maintainer for s390/pci, replacing Gerald Schaefer who
has moved his focus to s390/mm. Thank you Gerald!

Signed-off-by: Gerd Bayer <gbayer@linux.ibm.com>
Acked-by: Niklas Schnelle <schnelle@linux.ibm.com>
Acked-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

Author: Gerd Bayer

MAINTAINERS

@@ -23521,7 +23521,7 @@ F:	drivers/s390/net/
 
 S390 PCI SUBSYSTEM
 M:	Niklas Schnelle <schnelle@linux.ibm.com>
-M:	Gerald Schaefer <gerald.schaefer@linux.ibm.com>
+M:	Gerd Bayer <gbayer@linux.ibm.com>
 L:	linux-s390@vger.kernel.org
 S:	Supported
 F:	Documentation/arch/s390/pci.rst