IB/rxe: avoid unnecessary NULL check

Before goto err2, the variable qp is checked. So it is not necessary
to check qp in label err2.

Signed-off-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>