net/mlx5e: Fix endianness handling in pedit mask

The mask value is provided as 64 bit and has to be casted in
either 32 or 16 bit. On big endian systems the wrong half was
casted which resulted in an all zero mask.

Fixes: 2b64beba

 ("net/mlx5e: Support header re-write of partial fields in TC pedit offload")
Signed-off-by: Sebastian Hense <sebastian.hense1@ibm.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>