IB/rdmavt: Always return ERR_PTR from rvt_create_mmap_info()

The commit below modified rvt_create_mmap_info() to return ERR_PTR's but
didn't update the callers to handle them. Modify rvt_create_mmap_info() to
only return ERR_PTR and fix all error checking after
rvt_create_mmap_info() was called.

Fixes: ff23dfa13457 ("IB: Pass only ib_udata in function prototypes")
Link: https://lore.kernel.org/r/20200424173146.10970-1-sudipm.mukherjee@gmail.com
Cc: stable@vger.kernel.org [5.4+]
Tested-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Acked-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
diff --git a/drivers/infiniband/sw/rdmavt/qp.c b/drivers/infiniband/sw/rdmavt/qp.c
index 0e1b291..500a7ee 100644
--- a/drivers/infiniband/sw/rdmavt/qp.c
+++ b/drivers/infiniband/sw/rdmavt/qp.c
@@ -1244,8 +1244,8 @@ struct ib_qp *rvt_create_qp(struct ib_pd *ibpd,
 
 			qp->ip = rvt_create_mmap_info(rdi, s, udata,
 						      qp->r_rq.wq);
-			if (!qp->ip) {
-				ret = ERR_PTR(-ENOMEM);
+			if (IS_ERR(qp->ip)) {
+				ret = ERR_CAST(qp->ip);
 				goto bail_qpn;
 			}