jz4740: silence warnings related to mfd_get_cell changes

mfd_get_cell returns a const, so change the jz4740 clients to store
a const mfd cell.  This silences type mismatch warnings.
Signed-off-by: Andres Salomon <dilinger@queued.net>
Acked-by: Anton Vorontsov <cbouatmailru@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/hwmon/jz4740-hwmon.c

@@ -32,7 +32,7 @@ struct jz4740_hwmon {
 
 	int irq;
 
-	struct mfd_cell *cell;
+	const struct mfd_cell *cell;
 	struct device *hwmon;
 
 	struct completion read_completion;

drivers/power/jz4740-battery.c

@@ -39,7 +39,7 @@ struct jz_battery {
 	int irq;
 	int charge_irq;
 
-	struct mfd_cell *cell;
+	const struct mfd_cell *cell;
 
 	int status;
 	long voltage;