IB/mlx4: Initialize SRQ scatter entries when creating an SRQ

As for memfree mthca hardware, ConnectX also requires SRQ WQE scatter
entries to be initialized with the invalid L_Key at SRQ creation time.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>