RDMA/rxe: Missing unlock on error in get_srq_wqe()

This error path needs to unlock before returning.

Fixes: ec0fa244

 ("RDMA/rxe: Fix over copying in get_srq_wqe")
Link: https://lore.kernel.org/r/YNXUCmnPsSkPyhkm@mwanda
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Majd Dibbiny <majd@nvidia.com>
Reviewed-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>