MAINTAINERS: better list for "POSIX CLOCKS and TIMERS"

POSIX CLOCKS and TIMERS disscussion is more appropriate
on linux-kernel than linux-net. As suggested by the maintainer,
George Anzinger.

Signed-off-by: Horms <horms@verge.net.au>
Acked-by: George Anzinger <george@mvista.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>