vfio/pci: Fix error return code in vfio_ecap_init()

The error code returned from vfio_ext_cap_len() is stored in 'len', not
in 'ret'.

Fixes: 89e1f7d4c6 ("vfio: Add PCI device driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Message-Id: <20210515020458.6771-1-thunder.leizhen@huawei.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci_config.c

@@ -1581,7 +1581,7 @@ static int vfio_ecap_init(struct vfio_pci_device *vdev)
 			if (len == 0xFF) {
 				len = vfio_ext_cap_len(vdev, ecap, epos);
 				if (len < 0)
-					return ret;
+					return len;
 			}
 		}