When down_interruptible() or ib_post_send() failed in rdma_request(),
receive dma buffer is not unmapped. Add unmap action to error path.
Also if ib_post_recv() failed in post_recv(), dma buffer is not unmapped.
Add unmap action to error path.

Link: https://lkml.kernel.org/r/20230104020424.611926-1-shaozhengchao@huawei.com
Fixes: fc79d4b1 ("9p: rdma: RDMA Transport Support for 9P")
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>