can: c_can: fix error checking of priv->instance in probe()

This patch adds a type cast from 'unsigned int' to 'int'.

'priv->instance' may less than zero, so need a type cast, the related
warnings (allmodconfig, "EXTRA_CFLAGS=-W"):

  drivers/net/can/c_can/c_can_platform.c:198:3: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/c_can/c_can_platform.c

@@ -195,7 +195,7 @@ static int c_can_plat_probe(struct platform_device *pdev)
 
 		res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
 		priv->raminit_ctrlreg = devm_ioremap_resource(&pdev->dev, res);
-		if (IS_ERR(priv->raminit_ctrlreg) || priv->instance < 0)
+		if (IS_ERR(priv->raminit_ctrlreg) || (int)priv->instance < 0)
 			dev_info(&pdev->dev, "control memory is not used for raminit\n");
 		else
 			priv->raminit = c_can_hw_raminit;