net/mlx5: DR, Fix NULL vs IS_ERR checking in dr_domain_init_resources

The mlx5_get_uars_page() function  returns error pointers.
Using IS_ERR() to check the return value to fix this.

Fixes: 4ec9e7b0 ("net/mlx5: DR, Expose steering domain functionality")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/steering/dr_domain.c

@@ -2,6 +2,7 @@
 /* Copyright (c) 2019 Mellanox Technologies. */
 
 #include <linux/mlx5/eswitch.h>
+#include <linux/err.h>
 #include "dr_types.h"
 
 #define DR_DOMAIN_SW_STEERING_SUPPORTED(dmn, dmn_type)	\
@@ -72,9 +73,9 @@ static int dr_domain_init_resources(struct mlx5dr_domain *dmn)
 	}
 
 	dmn->uar = mlx5_get_uars_page(dmn->mdev);
-	if (!dmn->uar) {
+	if (IS_ERR(dmn->uar)) {
 		mlx5dr_err(dmn, "Couldn't allocate UAR\n");
-		ret = -ENOMEM;
+		ret = PTR_ERR(dmn->uar);
 		goto clean_pd;
 	}