iwlcore: Fix stay in table function.

Function rs_stay_in_table was flushing the rate scale table way to early. time_after
macro in expecting long value and was failing because we passing u32 value.

Signed-off-by: Mohamed Abbas <mohamed.abbas@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>