iwlwifi: Added foreward declaration for iwl_cfg in op_mode

Please merge this with "iwlwifi: op_mode holds its pointer
to the config"

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-op-mode.h b/drivers/net/wireless/iwlwifi/iwl-op-mode.h
index 73e1a0e..4ef742b 100644
--- a/drivers/net/wireless/iwlwifi/iwl-op-mode.h
+++ b/drivers/net/wireless/iwlwifi/iwl-op-mode.h
@@ -69,6 +69,7 @@
 struct iwl_device_cmd;
 struct iwl_rx_cmd_buffer;
 struct iwl_fw;
+struct iwl_cfg;
 
 /**
  * DOC: Operational mode - what is it ?