vdd_usb must not be present unless vdda1v8 is present. So, as vdda1v8 is
disabled during standby, vdd_usb cannot be kept on during suspend.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Change-Id: I49d9683fd2ca7f89cf17cc3147585fc6b8916388