[media] st_rc: fix build warning

Building for avr32 leads the following build warning:

drivers/media/rc/st_rc.c:270: warning: passing argument 1 of 'IS_ERR' discards qualifiers from pointer target type
drivers/media/rc/st_rc.c:271: warning: passing argument 1 of 'PTR_ERR' discards qualifiers from pointer target type

devm_ioremap_resource() returns void __iomem *, so change 'base' and
'rx_base' definitions accordingly.

Reported-by: kbuild test robot <[e-mail]>
Signed-off-by: Fabio Estevam <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/rc/st_rc.c

···
 	int				irq;
 	int				irq_wake;
 	struct clk			*sys_clock;
-	volatile void __iomem		*base;	/* Register base address */
-	volatile void __iomem		*rx_base;/* RX Register base address */
+	void __iomem			*base;	/* Register base address */
+	void __iomem			*rx_base;/* RX Register base address */
 	struct rc_dev			*rdev;
 	bool				overclocking;
 	int				sample_mult;
···
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 
 	rc_dev->base = devm_ioremap_resource(dev, res);
-	if (IS_ERR((__force void *)rc_dev->base)) {
-		ret = PTR_ERR((__force void *)rc_dev->base);
+	if (IS_ERR(rc_dev->base)) {
+		ret = PTR_ERR(rc_dev->base);
 		goto err;
 	}