usb: dwc3: omap: Don't set POWERPRESENT

TRM [1] recommends that POWERPRESENT bit must not be
set and left at it's default value of 0.

[1] OMAP542x TRM - http://www.ti.com/lit/pdf/swpu249


Section 23.11.4.5.1 Mailbox VBUS/ID Management

"Because PIPE powerpresent has a different meaning in host and in device mode,
and because of the redundancy with the UTMI signals, the controller ORes
together the appropriate PIPE and UTMI inputs to create its internal
VBUS status. For that reason, it is recommended to leave field
USBOTGSS_UTMI_OTG_STATUS[9] POWERPRESENT at its default value (=0), and only to
fill in the USB2 VBUS status fields in the same register."

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>