phy: usbphyc: use regulator_set_enable_if_allowed for disabling vdd supply

phy: usbphyc: use regulator_set_enable_if_allowed for disabling vdd supply

Use regulator_set_enable_if_allowed() api instead of regulator_set_enable()
while disabling vdd supply. This way the driver doesn't see an error
when disabling an always-on regulator.

This patch is needed since the commit f93fab312615 ("Revert 'power:
regulator: Return success on attempt to disable an always-on regulator'")
and use the API introduced by commit cc4a224af226 ("power: regulator:
Introduce regulator_set_enable_if_allowed api").

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>