net/mlx5: SF, Fix error return code in mlx5_sf_dev_probe()

Fix to return negative error code -ENOMEM from the ioremap() error
handling case instead of 0, as done elsewhere in this function.

Fixes: 1958fc2f ("net/mlx5: SF, Add auxiliary device driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>