[ARM] 3018/1: S3C2410 - check de-referenced device is really a platform device

Patch from Ben Dooks

Check that the device we are looking at is really
a platform device before trying to cast it to one
to find out the platform bus number.

Thanks to RMK for pointing this out.
Signed-off-by: NBen Dooks <ben-linux@fluff.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-s3c2410/clock.c

@@ -98,7 +98,10 @@ struct clk *clk_get(struct device *dev, const char *id)
 	struct clk *clk = ERR_PTR(-ENOENT);
 	int idno;
 
-	idno = (dev == NULL) ? -1 : to_platform_device(dev)->id;
+	if (dev == NULL || dev->bus != &platform_bus_type)
+		idno = -1;
+	else
+		idno = to_platform_device(dev)->id;
 
 	down(&clocks_sem);