MAINTAINERS: Update paths for main loop

Moved by c2b38b2 ("block: move AioContext, QEMUTimer, main-loop to
libqemuutil"), let's update MAINTAINERS too.

Reported-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

MAINTAINERS

@@ -1305,8 +1305,8 @@ Main loop
 M: Paolo Bonzini <pbonzini@redhat.com>
 S: Maintained
 F: cpus.c
-F: main-loop.c
-F: qemu-timer.c
+F: util/main-loop.c
+F: util/qemu-timer.c
 F: vl.c
 
 Human Monitor (HMP)