memory: renesas-rpc-if: fix possible NULL pointer dereference of resource

The platform_get_resource_byname() can return NULL which would be
immediately dereferenced by resource_size().  Instead dereference it
after validating the resource.

Addresses-Coverity: Dereference null return value
Fixes: ca7d8b98 ("memory: add Renesas RPC-IF driver")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210407154357.70200-1-krzysztof.kozlowski@canonical.com

drivers/memory/renesas-rpc-if.c

@@ -192,10 +192,10 @@ int rpcif_sw_init(struct rpcif *rpc, struct device *dev)
 	}
 
 	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "dirmap");
-	rpc->size = resource_size(res);
 	rpc->dirmap = devm_ioremap_resource(&pdev->dev, res);
 	if (IS_ERR(rpc->dirmap))
 		rpc->dirmap = NULL;
+	rpc->size = resource_size(res);
 
 	rpc->rstc = devm_reset_control_get_exclusive(&pdev->dev, NULL);