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

stable inclusion
from linux-4.19.194
commit c953aee0d8a162d249dedaa47111e95dde0461cd

--------------------------------

[ Upstream commit d1ce2c79 ]

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

Fixes: 89e1f7d4 ("vfio: Add PCI device driver")
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NZhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: NMax Gurtovoy <mgurtovoy@nvidia.com>
Message-Id: <20210515020458.6771-1-thunder.leizhen@huawei.com>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/vfio/pci/vfio_pci_config.c

@@ -1574,7 +1574,7 @@ 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;
 			}
 		}