hmp-commands-info: Change "@Findex FOO" to "@Findex info FOO"

qemu-doc has the monitor commands in the "Function Index".  The "info
FOO" are listed as "FOO" there.  List them as "info FOO" instead.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20171002134538.23332-4-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>