i2c-pxa: Fix adapter number

It turns out that platform_device.id is a "u32" so testing it for being
nonnegative is useless when setting up an i2c adapte.  Instead,
do what the platform_bus code does and test it against the value "-1".
Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/i2c/busses/i2c-pxa.c

@@ -926,7 +926,7 @@ static int i2c_pxa_probe(struct platform_device *dev)
 	 * The reason to do so is to avoid sysfs names that only make
 	 * sense when there are multiple adapters.
 	 */
-	i2c->adap.nr = dev->id >= 0 ? dev->id : 0;
+	i2c->adap.nr = dev->id != -1 ? dev->id : 0;
 
 	ret = i2c_add_numbered_adapter(&i2c->adap);
 	if (ret < 0) {