iwlwifi: include debugfs.h

The iwl-op-mode.h file uses a struct dentry for debugfs
so should include debugfs.h.
Reviewed-by: NEmmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

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;