net/mlx5: Fix false compilation warning

Fix the following warning:
drivers/net/ethernet/mellanox/mlx5/core//fs_core.c:845:5:
warning: 'err' may be used uninitialized in this function
[-Wmaybe-uninitialized]

No real issue here. This is only a false compiler warning.
The 'err' variable is guaranteed to be init by time of usage.

gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-4)
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Reviewed-by: Alex Vesker <valex@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/fs_core.c

@@ -810,7 +810,7 @@ static int update_root_ft_create(struct mlx5_flow_table *ft, struct fs_prio
 	struct mlx5_flow_root_namespace *root = find_root(&prio->node);
 	struct mlx5_ft_underlay_qp *uqp;
 	int min_level = INT_MAX;
-	int err;
+	int err = 0;
 	u32 qpn;
 
 	if (root->root_ft)