PCI: imx6: Move imx6_pcie_enable_ref_clk() earlier

Move imx6_pcie_enable_ref_clk() earlier so it's not in the middle between
imx6_pcie_assert_core_reset() and imx6_pcie_deassert_core_reset().  No
functional change intended.

Link: https://lore.kernel.org/r/1657783869-19194-4-git-send-email-hongxing.zhu@nxp.com


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Richard Zhu <hongxing.zhu@nxp.com>