ARM: OMAP: Fix devexit for dma when CONFIG_HOTPLUG is not set

Otherwise we get:

`omap_system_dma_remove' referenced in section `.data' of arch/arm/plat-omap/built-in.o:
defined in discarded section `.devexit.text' of arch/arm/plat-omap/built-in.o
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/plat-omap/dma.c

@@ -2125,7 +2125,7 @@ static int __devexit omap_system_dma_remove(struct platform_device *pdev)
 
 static struct platform_driver omap_system_dma_driver = {
 	.probe		= omap_system_dma_probe,
-	.remove		= omap_system_dma_remove,
+	.remove		= __devexit_p(omap_system_dma_remove),
 	.driver		= {
 		.name	= "omap_dma_system"
 	},