usbphyc is a 48Mhz clock provider: the clock can be used as clock source
for USB OTG. Add #clock-cells property to usbphyc node to reflect this
capability.
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>