timer: mtk: skip setting parent with dummy fixed-clock

timer: mtk: skip setting parent with dummy fixed-clock

Skip setting parent with dummy fixed-clock. Upstream linux might declare
an additional clock for the mtk timer and that additional clock might
also be a fixed-clock defined in DT. Setting parent of a dummy fixed-clock
resulta in error hence mtk timer fails to probe.

Skip setting parent to permit correct probe of the mtk timer.

Fixes: d3c3606c5cc6 ("timer: MediaTek: add timer driver for MediaTek SoCs")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>