IB/rxe: avoid srq memory leak

In rxe_queue_init, q and q->buf are allocated. In do_mmap_info, q->ip is
allocated. When error occurs, rxe_srq_from_init and the later error
handler do not free these allocated memories.  This will make memory leak.

Signed-off-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>