MAINTAINERS: add git url entry for UIO

Added git url for UIO section.

Signed-off-by: Mandeep Sandhu <mandeep.sandhu@cyaninc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>