MAINTAINERS: include governors into CPU IDLE TIME MANAGEMENT FRAMEWORK

The current pattern in the file entry does not make the files in the
governors subdirectory to be a part of the CPU IDLE TIME MANAGEMENT
FRAMEWORK.

Adjust the file pattern to include files in governors.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>