backlight: mp3309c: Fix signedness bug in mp3309c_parse_fwnode()

The "num_levels" variable is used to store error codes from
device_property_count_u32() so it needs to be signed.  This doesn't
cause an issue at runtime because devm_kcalloc() won't allocate negative
sizes.  However, it's still worth fixing.

Fixes: b54c828b ("backlight: mp3309c: Make use of device properties")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Tested-by: Flavio Suligoi <f.suligoi@asem.it>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/74347f67-360d-4513-8939-595e3c4764fa@moroto.mountainSigned-off-by: Lee Jones <lee@kernel.org>

drivers/video/backlight/mp3309c.c

@@ -205,8 +205,9 @@ static int mp3309c_parse_fwnode(struct mp3309c_chip *chip,
 				struct mp3309c_platform_data *pdata)
 {
 	int ret, i;
-	unsigned int num_levels, tmp_value;
+	unsigned int tmp_value;
 	struct device *dev = chip->dev;
+	int num_levels;
 
 	if (!dev_fwnode(dev))
 		return dev_err_probe(dev, -ENODEV, "failed to get firmware node\n");