RDMA/rtrs: server: Fix some error return code

RDMA/rtrs: server: Fix some error return code

Fix to return negative error code -ENOMEM from the some error handling
cases instead of 0, as done elsewhere in this function.

Fixes: b5ef0cd050ee ("RDMA/rtrs: server: main functionality")
Fixes: 93e3b20d5c33 ("RDMA/rtrs: server: sysfs interface functions")
Link: https://lore.kernel.org/r/20200519091912.134358-1-weiyongjun1@huawei.com
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Danil Kipnis <danil.kipnis@cloud.ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>