thermal: armada: fix legacy validity test sense

Commit 8c0e64a ("thermal: armada: get rid of the ->is_valid()
pointer") removed the unnecessary indirection through a function
pointer, but in doing so, also removed the negation operator too:

-       if (priv->data->is_valid && !priv->data->is_valid(priv)) {
+       if (armada_is_valid(priv)) {

which results in:

armada_thermal f06f808c.thermal: Temperature sensor reading not valid
armada_thermal f240007.thermal: Temperature sensor reading not valid
armada_thermal f4400078.thermal: Temperature sensor reading not valid

at boot, or whenever the "temp" sysfs file is read.  Replace the
negation operator.

Fixes: 8c0e64a ("thermal: armada: get rid of the ->is_valid() pointer")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

drivers/thermal/armada_thermal.c

@@ -357,7 +357,7 @@ static int armada_get_temp_legacy(struct thermal_zone_device *thermal,
 	int ret;
 
 	/* Valid check */
-	if (armada_is_valid(priv)) {
+	if (!armada_is_valid(priv)) {
 		dev_err(priv->dev,
 			"Temperature sensor reading not valid\n");
 		return -EIO;