net/mlx5e: Ethtool steering, fix udp source port value

Copy and paste bug was introduced in the offending patch.
We need to write udp source port value into the headers value and not
headers criteria "mask".

Fixes: 142644f8

 ("net/mlx5e: Ethtool steering flow parsing refactoring")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>