drivers/usb/host: Use an IS_ERR test rather than a NULL test

In case of error, the function isp1760_register returns an ERR pointer, but never returns a NULL pointer. So after a call to this function, a NULL test should be replaced by an IS_ERR test. Moreover, we have noticed that:
(1) the result of isp1760_register is assigned through the function pci_set_drvdata without an error test,
(2) if the call to isp1760_register fails, the current function (isp1761_pci_probe) returns 0, and if it succeeds, it returns -ENOMEM, which seems odd.

Thus, we suggest to move the test before the call to pci_set_drvdata to correct (1), and to turn it into a non IS_ERR test to correct (2).

The semantic match that finds this problem is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@bad_null_test@
expression x,E;
statement S1, S2;
@@
x = isp1760_register(...)
... when != x = E
* if (x = NULL)
S1 else S2
// </smpl>

---
 drivers/usb/host/isp1760-if.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff -u -p a/drivers/usb/host/isp1760-if.c b/drivers/usb/host/isp1760-if.c
@@ -232,9 +232,10 @@ static int __devinit isp1761_pci_probe(s
 	hcd = isp1760_register(pci_mem_phy0, length, dev->irq,
 		IRQF_SHARED | IRQF_DISABLED, &dev->dev, dev_name(&dev->dev),
 		devflags);
-	pci_set_drvdata(dev, hcd);
-	if (!hcd)
+	if (!IS_ERR(hcd)) {
+		pci_set_drvdata(dev, hcd);
 		return 0;
+	}
 clean:
 	status = -ENODEV;
 	iounmap(iobase);