clk: spacemit: k3: Switch to pll2_d6 as parent for PCIe clock

clk: spacemit: k3: Switch to pll2_d6 as parent for PCIe clock

According to SpacemiT updated docs, the PCIe master and slave clock's
parent is the pll2_d6 clock, so fix it.

Fixes: e371a77255b8 ("clk: spacemit: k3: add the clock tree")
Link: https://patch.msgid.link/20260511-06-pci-clk-fix-v2-1-c9a5e563bab3@kernel.org
Signed-off-by: Yixun Lan <dlan@kernel.org>