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>
diff --git a/drivers/power/jz4740-battery.c b/drivers/power/jz4740-battery.c
index 0938650..763f894 100644
--- a/drivers/power/jz4740-battery.c
+++ b/drivers/power/jz4740-battery.c
@@ -39,7 +39,7 @@
 	int irq;
 	int charge_irq;
 
-	struct mfd_cell *cell;
+	const struct mfd_cell *cell;
 
 	int status;
 	long voltage;