RDMA/nes: Write correct register write to set TX pause param

Setting TX pause param writes to the wrong register location causing
the adapter to hang.  Correct the define used to write the reigster.

Addresses: https://bugs.openfabrics.org/show_bug.cgi?id=2116


Reported-by: Shiri Franchi <shirif@voltaire.com>
Signed-off-by: Chien Tung <chien.tin.tung@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>