livepatch: Update maintainers

Seth and Vojtech are no longer active maintainers of livepatch, so
remove them in favor of Jessica and Miroslav.

Also add Petr as a designated reviewer.

[jikos@kernel.org: Petr is the only one affected who hasn't provided his
 Ack by the time this patch has been applied, as he is offline curently;
 but I hereby assert that I've talked to him and he's OK with this change]
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Seth Jennings <sjenning@redhat.com>
Acked-by: Jessica Yu <jeyu@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Vojtech Pavlik <vojtech@suse.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>