scripts/add_maintainers.pl: Don't call get_maintainers.pl with -f

scripts/add_maintainers.pl: Don't call get_maintainers.pl with -f

The option -f of scripts/get_maintainers.pl will return the maintainers
of a given file, *not* the list of maintainers if the file was a patch.

The output expected of add_maintainers is the latter, so drop the option
-f.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Lars Kurth <lars.kurth@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>