intel_idle: Fix a cast to pointer from integer of different size warning in intel_idle

Fix the following warning:

drivers/idle/intel_idle.c: In function 'intel_idle_cpuidle_devices_init':
drivers/idle/intel_idle.c:518:5: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]

By making get_driver_data() return a long instead of an int.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>