nvme-rdma: fix the return value of nvme_rdma_reinit_request()

PTR_ERR should be applied before its argument is reassigned, otherwise the
return value will be set to 0, not error code.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: Jay Freyensee <james_p_freyensee@linux.intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>