iwl3945: use cancel_delayed_work_sync to cancel rfkill_poll
iwl3945: use cancel_delayed_work_sync to cancel rfkill_poll

Users reported lockup with work still trying to run
after module has been unloaded.

http://thread.gmane.org/gmane.linux.kernel.wireless.general/30594/focus=30601

Signed-off-by: Reinette Chatre <bb5db0b6f994551e9583fc9e712e27afb43f1dec@intel.com>
Reported-by: TJ <24bf68e341ce0fbd9259a5d51feed79682ea4eba@tjworld.net>
Reported-by: Huaxu Wan <a4b6c5f1d8cd2f42cfcb3e50e4d7b2e4e4f38d1c@linux.intel.com>
Signed-off-by: John W. Linville <2a53bac7a5d324865ef46ec4c38b2c0fba1456b4@tuxdriver.com>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs