drivers/block/xsysace.c: fix id with missing port-number

If the port number is missing from the device-tree the device gets named
xs` instead of xsa.  This fixes the check for missing ids.

Tested on ml507 board.
Signed-off-by: NGernot Vormayr <gvormayr@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/block/xsysace.c

@@ -1160,8 +1160,7 @@ static int ace_probe(struct platform_device *dev)
 	dev_dbg(&dev->dev, "ace_probe(%p)\n", dev);
 
 	/* device id and bus width */
-	of_property_read_u32(dev->dev.of_node, "port-number", &id);
-	if (id < 0)
+	if (of_property_read_u32(dev->dev.of_node, "port-number", &id))
 		id = 0;
 	if (of_find_property(dev->dev.of_node, "8-bit", NULL))
 		bus_width = ACE_BUS_WIDTH_8;