usb: musb: dsps: fix the base address for accessing the mode register

commit 943c1397 "usb: musb: dsps: implement ->set_mode()"
should have made it possible to use the driver with boards that have
the USBID pin unconnected. This doesn't actually work, since the
driver uses the wrong base address to access the mode register.
Furthermore it uses different base addresses in different places to
access the same register (phy_utmi).

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>