NIU: fix incorrect error return, missed in previous revert

Commit 7930742d, reverting 26fd962b, missed out on reverting an incorrect
change to a return value.  The niu_pci_vpd_scan_props(..) == 1 case appears
to be a normal path - treating it as an error and return -EINVAL was
breaking VPD_SCAN and causing the driver to fail to load.

Fix, so my Neptune card works again.

Cc: Kangjie Lu <kjlu@umn.edu>
Cc: Shannon Nelson <shannon.lee.nelson@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: stable <stable@vger.kernel.org>
Fixes: 7930742d ('Revert "niu: fix missing checks of niu_pci_eeprom_read"')
Signed-off-by: Paul Jakma <paul@jakma.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sun/niu.c

@@ -8191,8 +8191,9 @@ static int niu_pci_vpd_fetch(struct niu *np, u32 start)
 		err = niu_pci_vpd_scan_props(np, here, end);
 		if (err < 0)
 			return err;
+		/* ret == 1 is not an error */
 		if (err == 1)
-			return -EINVAL;
+			return 0;
 	}
 	return 0;
 }