iwlwifi: small compile warnings without CONFIG_IWLWIFI_DEBUG

CC [M]  drivers/net/wireless/iwlwifi/iwl-scan.o
drivers/net/wireless/iwlwifi/iwl-scan.c: In function 'iwl_rx_scan_complete_notif':
drivers/net/wireless/iwlwifi/iwl-scan.c:274: warning: unused variable 'scan_notif'

Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Tomas Winkler <tomasw@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>