get_maintainer: fix perl 5.22/5.24 deprecated/incompatible "\C" use

get_maintainer: fix perl 5.22/5.24 deprecated/incompatible "\C" use

Perl 5.22 emits a deprecated message when "\C" is used in a regex.  Perl
5.24 will disallow it altogether.

Fix it by using [A-Z] instead of \C.

 [ Upstream commit ce8155f7a3d59ce868ea16d8891edda4d865e873 ]

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Keir Fraser <keir@xen.org>
Cc: Tim Deegan <tim@xen.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>