powerpc/fsl-rio: Fix fsl_rio_setup error paths and use-after-unmap

Several of the error paths from fsl_rio_setup are missing error
messages.

Worse, fsl_rio_setup initializes several global pointers and does not
NULL them out after freeing/unmapping on error. This caused
fsl_rio_mcheck_exception() to crash when accessing rio_regs_win which
was non-NULL but had been unmapped.

Signed-off-by: Scott Wood <[e-mail]>
Cc: Liu Gang <[e-mail]>
---
Liu Gang, are you sure all of these error conditions are fatal? Why
does the rio driver fail if rmu is not present (e.g. on t4240)?

arch/powerpc/sysdev/fsl_rio.c

···
 	ops->get_inb_message = fsl_get_inb_message;
 
 	rmu_node = of_parse_phandle(dev->dev.of_node, "fsl,srio-rmu-handle", 0);
-	if (!rmu_node)
+	if (!rmu_node) {
+		dev_err(&dev->dev, "No valid fsl,srio-rmu-handle property\n");
 		goto err_rmu;
+	}
 	rc = of_address_to_resource(rmu_node, 0, &rmu_regs);
 	if (rc) {
 		dev_err(&dev->dev, "Can't get %s property 'reg'\n",
···
 	/*set up doobell node*/
 	np = of_find_compatible_node(NULL, NULL, "fsl,srio-dbell-unit");
 	if (!np) {
+		dev_err(&dev->dev, "No fsl,srio-dbell-unit node\n");
 		rc = -ENODEV;
 		goto err_dbell;
 	}
···
 	/*set up port write node*/
 	np = of_find_compatible_node(NULL, NULL, "fsl,srio-port-write-unit");
 	if (!np) {
+		dev_err(&dev->dev, "No fsl,srio-port-write-unit node\n");
 		rc = -ENODEV;
 		goto err_pw;
 	}
···
 	return 0;
 err:
 	kfree(pw);
+	pw = NULL;
 err_pw:
 	kfree(dbell);
+	dbell = NULL;
 err_dbell:
 	iounmap(rmu_regs_win);
+	rmu_regs_win = NULL;
 err_rmu:
 	kfree(ops);
 err_ops:
 	iounmap(rio_regs_win);
+	rio_regs_win = NULL;
 err_rio_regs:
 	return rc;
 }