MAINTAINERS: update my email address

My Citrix email address will expire shortly.
Signed-off-by: NPaul Durrant <paul.durrant@citrix.com>
Reviewed-by: NAnthony PERARD <anthony.perard@citrix.com>
Message-Id: <20190913122418.848-1-paul.durrant@citrix.com>
Signed-off-by: NAnthony PERARD <anthony.perard@citrix.com>

MAINTAINERS

@@ -406,7 +406,7 @@ Guest CPU Cores (Xen)
 X86 Xen CPUs
 M: Stefano Stabellini <sstabellini@kernel.org>
 M: Anthony Perard <anthony.perard@citrix.com>
-M: Paul Durrant <paul.durrant@citrix.com>
+M: Paul Durrant <paul@xen.org>
 L: xen-devel@lists.xenproject.org
 S: Supported
 F: */xen*