phy: meson-axg-mipi: Access parent ofnode through dev_ofnode()

With commit 84a42ae3 ("dm: core: Rename device node to indicate it
is private") and commit f10643cf ("dm: core: Access device ofnode
through functions") accesses to the "node" member were replaced with
dev_ofnode(). Also apply that replacement here.

Fixes: 4547551a ("phy: Add Amlogic AXG MIPI PCIe Analog PHY driver")
Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>