MAINTAINERS: Remove Stephen Bates as Microsemi Switchtec maintainer

Just sent an email there and received an autoreply because he no longer
works there.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

MAINTAINERS

@@ -10314,7 +10314,6 @@ F:	drivers/pci/host/vmd.c
 
 PCI DRIVER FOR MICROSEMI SWITCHTEC
 M:	Kurt Schwemmer <kurt.schwemmer@microsemi.com>
-M:	Stephen Bates <stephen.bates@microsemi.com>
 M:	Logan Gunthorpe <logang@deltatee.com>
 L:	linux-pci@vger.kernel.org
 S:	Maintained