PCI: imx6: Invoke the PHY exit function after PHY power off

To balance phy->init_count, invoke the phy_exit() after phy_power_off().

Link: https://lore.kernel.org/r/1646289275-17813-1-git-send-email-hongxing.zhu@nxp.com


Fixes: 178e244c ("PCI: imx: Add the imx8mm pcie support")
Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>