w1: Silence ds1wm warnings related to mfd_get_cell changes

mfd_get_cell returns a const, so change the ds1wm client to store
a const mfd cell.  This silences type mismatch warnings.

Since we're guaranteed to have the mfd_cell, we can also simplify
the code a bit to get rid of a temporary variable and NULL check.
Signed-off-by: NAndres Salomon <dilinger@queued.net>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

drivers/w1/masters/ds1wm.c

@@ -90,7 +90,7 @@ struct ds1wm_data {
 	void		__iomem *map;
 	int		bus_shift; /* # of shifts to calc register offsets */
 	struct platform_device *pdev;
-	struct mfd_cell	*cell;
+	const struct mfd_cell *cell;
 	int		irq;
 	int		active_high;
 	int		slave_present;
@@ -330,16 +330,11 @@ static int ds1wm_probe(struct platform_device *pdev)
 	struct ds1wm_data *ds1wm_data;
 	struct ds1wm_driver_data *plat;
 	struct resource *res;
-	struct mfd_cell *cell;
 	int ret;
 
 	if (!pdev)
 		return -ENODEV;
 
-	cell = mfd_get_cell(pdev);
-	if (!cell)
-		return -ENODEV;
-
 	ds1wm_data = kzalloc(sizeof(*ds1wm_data), GFP_KERNEL);
 	if (!ds1wm_data)
 		return -ENOMEM;
@@ -362,7 +357,7 @@ static int ds1wm_probe(struct platform_device *pdev)
 	ds1wm_data->bus_shift = resource_size(res) >> 3;
 
 	ds1wm_data->pdev = pdev;
-	ds1wm_data->cell = cell;
+	ds1wm_data->cell = mfd_get_cell(pdev);
 
 	res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
 	if (!res) {