RDMA/cm: Fix an error check in cm_alloc_id_priv()

The xa_alloc_cyclic_irq() function returns either 0 or 1 on success and
negatives on error.  This code treats 1 as an error and returns ERR_PTR(1)
which will cause an Oops in the caller.

Fixes: ae78ff3a

 ("RDMA/cm: Convert local_id_table to XArray")
Link: https://lore.kernel.org/r/20200407093714.GA80285@mwanda
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>