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

stable inclusion
from stable-v5.10.90
commit 4cd1da02f0c39606e3378c9255f17d6f85d106c7
bugzilla: 186168 https://gitee.com/openeuler/kernel/issues/I4SHY1

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4cd1da02f0c39606e3378c9255f17d6f85d106c7



--------------------------------

[ Upstream commit 6b8b4258 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>