rtc: update maintainership of pxa rtc driver

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>