net/mlx5: E-Switch, Fix an Oops in error handling code

The error handling dereferences "vport".  There is nothing we can do if
it is an error pointer except returning the error code.

Fixes: 133dcfc5

 ("net/mlx5: E-Switch, Alloc and free unique metadata for match")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>