net: mlx5: Fix Kconfig help text

Since the following commit, Infiniband and Ethernet have not been
mutually exclusive.

Fixes: 4aa17b28

 mlx5: Enable mutual support for IB and Ethernet
Signed-off-by: Christopher Covington <cov@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>