Fix debugfs_create_bool's error checking method for wireless/iwlwifi/

debugfs_create_bool() returns NULL if an error occurs, returns -ENODEV
when debugfs is not enabled in the kernel.
Signed-off-by: NZhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-debugfs.c

@@ -58,7 +58,8 @@
 #define DEBUGFS_ADD_BOOL(name, parent, ptr) do {                        \
 	dbgfs->dbgfs_##parent##_files.file_##name =                     \
 	debugfs_create_bool(#name, 0644, dbgfs->dir_##parent, ptr);     \
-	if (IS_ERR(dbgfs->dbgfs_##parent##_files.file_##name))          \
+	if (IS_ERR(dbgfs->dbgfs_##parent##_files.file_##name)		\
+			|| !dbgfs->dbgfs_##parent##_files.file_##name)	\
 		goto err;                                               \
 } while (0)