clk: mediatek: drop parent udevice field

clk: mediatek: drop parent udevice field

Remove the parent field from the mediatek clock private data structures.
This was no longer used other than debug prints.

The uclass_get_device_* functions had the effect of ensuring that
parents were probed. This is done now by having parent providers
probe on bind, so re-probing here is no longer necessary. Clock trees
could have more than one parent anyway, so the existing code was not
completely correct anyway.

Link: https://patch.msgid.link/20260710-mtk-clk-parent-lookup-improvements-v2-19-f3f3a4a28dca@baylibre.com
Signed-off-by: David Lechner <dlechner@baylibre.com>