phy: stm32: register usbphyc as clock provider of ck_usbo_48m clock

ck_usbo_48m is generated by usbphyc PLL and used by OTG controller
for Full-Speed use cases with dedicated Full-Speed transceiver.

ck_usbo_48m is available as soon as the PLL is enabled.

Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20210208114659.15269-3-amelie.delaunay@foss.st.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>