net/mlx5: DR: Fix incorrect type in return expression

dr_ste_crc32_calc() calculates crc32 and should return it in HW format.
It is being used to calculate a u32 index, hence we force the return value
of u32 to avoid the sparse warning:

drivers/net/ethernet/mellanox/mlx5/core/steering/dr_ste.c:115:16:
warning: incorrect type in return expression (different base types)
    expected unsigned int
    got restricted __be32 [usertype]

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>