IB/mlx4: Fix error path in create_qp_common()

    
The error handling code at err_wrid in create_qp_common() does not
handle a userspace QP attached to an SRQ correctly, since it ends up
in the else clause of the if statement.  This means it tries to
kfree() the uninitialized qp->sq.wrid and qp->rq.wrid pointers.  Fix
this so we only free the wrid arrays for kernel QPs.

Pointed out by Michael S. Tsirkin <mst@dev.mellanox.co.il>.

Signed-off-by: Roland Dreier <rolandd@cisco.com>