mfd: max8998: Naturalise cross-architecture discrepancies

If we compile the MAX8998 for a 64bit architecture we receive the following
warnings:

  drivers/mfd/max8998.c: In function ‘max8998_i2c_get_driver_data’:
  drivers/mfd/max8998.c:178:10:
    warning: cast from pointer to integer of different size
     return (int)match->data;
            ^

Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/max8998.c b/drivers/mfd/max8998.c
index 612ca40..5d5e186 100644
--- a/drivers/mfd/max8998.c
+++ b/drivers/mfd/max8998.c
@@ -169,16 +169,16 @@
 	return pd;
 }
 
-static inline int max8998_i2c_get_driver_data(struct i2c_client *i2c,
+static inline unsigned long max8998_i2c_get_driver_data(struct i2c_client *i2c,
 						const struct i2c_device_id *id)
 {
 	if (IS_ENABLED(CONFIG_OF) && i2c->dev.of_node) {
 		const struct of_device_id *match;
 		match = of_match_node(max8998_dt_match, i2c->dev.of_node);
-		return (int)(long)match->data;
+		return (unsigned long)match->data;
 	}
 
-	return (int)id->driver_data;
+	return id->driver_data;
 }
 
 static int max8998_i2c_probe(struct i2c_client *i2c,