usb: dwc3: msm: Remove psy and regs from struct dwc3_otg

The regs field is unused, so remove it. The psy pointer to
the power_supply is simply the usb_psy in dwc3_msm, so use
that directly instead.

Change-Id: I091c67e49f19e09cc44575080fac42bd495ac651
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>