regulator: max8907: fix use of possibly NULL idata

If a regulator is not used by a board, it's quite legitimate not to
provide platform data or a device tree node to configure it (i.e.
regulator_init_data). In that case, during MAX8907 regulator's
probe(), the idata variable will be NULL for that regulator. Prevent
dereferincing it.

If the MBATT regulator's init_data is not specified, or no name was
specified in the constraints, the regulator will be named based on
the regulator descriptor, so initialize mbatt_rail_name from there.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/max8907-regulator.c

@@ -323,7 +323,10 @@ static __devinit int max8907_regulator_probe(struct platform_device *pdev)
 
 		switch (pmic->desc[i].id) {
 		case MAX8907_MBATT:
-			mbatt_rail_name = idata->constraints.name;
+			if (idata && idata->constraints.name)
+				mbatt_rail_name = idata->constraints.name;
+			else
+				mbatt_rail_name = pmic->desc[i].name;
 			break;
 		case MAX8907_BBAT:
 		case MAX8907_SDBY: