sky2: Remove redundant NULL check for debugfs_create_dir

Since debugfs_create_dir() returns ERR_PTR, IS_ERR() is enough to
check whether the directory is successfully created. So remove the
redundant NULL check.
Signed-off-by: Ruan Jinjie <ruanjinjie@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20230817073017.350002-1-ruanjinjie@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/marvell/sky2.c

@@ -4528,7 +4528,7 @@ static __init void sky2_debug_init(void)
 	struct dentry *ent;
 
 	ent = debugfs_create_dir("sky2", NULL);
-	if (!ent || IS_ERR(ent))
+	if (IS_ERR(ent))
 		return;
 
 	sky2_debug = ent;