net/mlx4: fix sparse warnings on wrong type for RSS keys

The keys used for the hardware RSS topelitz hash are of type __be32
where the values provided by the driver are from array of u32,
this triggered sparse warning on incorrect type in assignment as of different base types.
Since these values are picked randomly,
the fix is to transform the key to __be32 by executing cpu_to_be_32()

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>