i2c: Constify i2c_get_clientdata's parameter

i2c_get_clientdata doesn't change the i2c_client it is passed as a
parameter, so it can be constified. Same for i2c_get_adapdata.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
diff --git a/include/linux/device.h b/include/linux/device.h
index 987f591..1a3686d 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -450,7 +450,7 @@
 }
 #endif
 
-static inline void *dev_get_drvdata(struct device *dev)
+static inline void *dev_get_drvdata(const struct device *dev)
 {
 	return dev->driver_data;
 }