PCI: imx: Fix checking pd_pcie_phy device link addition

The check on the device_link_add() return value is wrong;
this leads to erroneous code execution, so fix it.

Fixes: 3f7cceea

 ("PCI: imx: Add multi-pd support")
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>