xprtrdma: Fix uninitialized variable

net/sunrpc/xprtrdma/frwr_ops.c:151:32: warning: variable 'rc' is uninitialized when used here [-Wuninitialized]
          trace_xprtrdma_frwr_alloc(mr, rc);
                                        ^~
  net/sunrpc/xprtrdma/frwr_ops.c:127:8: note: initialize the variable 'rc' to silence this warning
          int rc;
                ^
                 = 0
  1 warning generated.

The tracepoint is intended to record the error returned from
ib_alloc_mr(). In the current code there is no other purpose for
@rc, so simply replace it.
Reported-by: kernel test robot <lkp@intel.com>
Fixes: d8cf39a280c3b0 ('xprtrdma: MR-related memory allocation should be allowed to fail')
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/frwr_ops.c

@@ -124,7 +124,6 @@ int frwr_mr_init(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr *mr)
 	unsigned int depth = ep->re_max_fr_depth;
 	struct scatterlist *sg;
 	struct ib_mr *frmr;
-	int rc;
 
 	sg = kcalloc_node(depth, sizeof(*sg), XPRTRDMA_GFP_FLAGS,
 			  ibdev_to_node(ep->re_id->device));
@@ -148,7 +147,7 @@ int frwr_mr_init(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr *mr)
 
 out_mr_err:
 	kfree(sg);
-	trace_xprtrdma_frwr_alloc(mr, rc);
+	trace_xprtrdma_frwr_alloc(mr, PTR_ERR(frmr));
 	return PTR_ERR(frmr);
 }