mfd: wm8994-core: Naturalise cross-architecture discrepancies

If we compile the WM8994 for a 64bit architecture we receive the following
warnings:

drivers/mfd/wm8994-core.c: In function ‘wm8994_i2c_probe’:
drivers/mfd/wm8994-core.c:639:19:
  warning: cast from pointer to integer of different size
    wm8994->type = (int)of_id->data;
                   ^
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/wm8994-core.c

@@ -636,7 +636,7 @@ static int wm8994_i2c_probe(struct i2c_client *i2c,
 	if (i2c->dev.of_node) {
 		of_id = of_match_device(wm8994_of_match, &i2c->dev);
 		if (of_id)
-			wm8994->type = (int)of_id->data;
+			wm8994->type = (enum wm8994_type)of_id->data;
 	} else {
 		wm8994->type = id->driver_data;
 	}