Driver core: make struct platform_driver.id_table const

This fixes a warning on several pxa based machines:

	arch/arm/mach-pxa/ssp.c:475: warning: initialization discards qualifiers from pointer target type

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Vikram Dhillon <dhillonv10@gmail.com>
Acked-by: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
index 2c2d035..212da17 100644
--- a/include/linux/platform_device.h
+++ b/include/linux/platform_device.h
@@ -62,7 +62,7 @@
 	int (*suspend)(struct platform_device *, pm_message_t state);
 	int (*resume)(struct platform_device *);
 	struct device_driver driver;
-	struct platform_device_id *id_table;
+	const struct platform_device_id *id_table;
 };
 
 extern int platform_driver_register(struct platform_driver *);