phy: stm32-usbphyc: manage properly the clk identifier with CCF

phy: stm32-usbphyc: manage properly the clk identifier with CCF

Add private uclass data for "stm32-usbphyc-clk" as it is not done
by the driver model.

This clk struct is needed by CCF to save the unique id used to identify
each clock.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Lukasz Majewski <lukma@denx.de>
Cc: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>