iwl3945: clear scanning bits upon failure

This patch ensures we clear any scan status bit when
an error occurs while sending the scan command. It is
the implementation of patch:
"iwlwifi: clear scanning bits upon failure"
for iwl3945.

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>