usb: phy: msm: Vote for corner of VDD CX instead of voltage of VDD CX

New platform uses RBCPR hardware feature, with that voting for
absolute voltage of VDD CX is not required. Hence vote for corner of
VDD CX which uses nominal corner voltage on VDD CX.

Signed-off-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Cc: Mayank Rana <mrana@codeaurora.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>