wifi: rtw88: debug: Fix the NULL vs IS_ERR() bug for debugfs_create_file()

Since debugfs_create_file() return ERR_PTR and never return NULL, so use
IS_ERR() to check it instead of checking NULL.

Fixes: e3037485 ("rtw88: new Realtek 802.11ac driver")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230919050651.962694-1-ruanjinjie@huawei.com

drivers/net/wireless/realtek/rtw88/debug.c

@@ -1233,9 +1233,9 @@ static struct rtw_debugfs_priv rtw_debug_priv_dm_cap = {
 #define rtw_debugfs_add_core(name, mode, fopname, parent)		\
 	do {								\
 		rtw_debug_priv_ ##name.rtwdev = rtwdev;			\
-		if (!debugfs_create_file(#name, mode,			\
+		if (IS_ERR(debugfs_create_file(#name, mode,		\
 					 parent, &rtw_debug_priv_ ##name,\
-					 &file_ops_ ##fopname))		\
+					 &file_ops_ ##fopname)))	\
 			pr_debug("Unable to initialize debugfs:%s\n",	\
 			       #name);					\
 	} while (0)