arm64: dts: imx8m*venice: add missing clock-names to pcie_phy

Define the missing clock-names property for the pcie_phy required by
the fsl,imx8-pcie-phy dt bindings.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>