iwlwifi: include debugfs.h

The iwl-op-mode.h file uses a struct dentry for debugfs
so should include debugfs.h.

Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-op-mode.h b/drivers/net/wireless/iwlwifi/iwl-op-mode.h
index b661564..dc79258 100644
--- a/drivers/net/wireless/iwlwifi/iwl-op-mode.h
+++ b/drivers/net/wireless/iwlwifi/iwl-op-mode.h
@@ -63,6 +63,8 @@
 #ifndef __iwl_op_mode_h__
 #define __iwl_op_mode_h__
 
+#include <linux/debugfs.h>
+
 struct iwl_op_mode;
 struct iwl_trans;
 struct sk_buff;