usb: dwc3-msm: Set vbus_active in peripheral only mode

The recent change in commit 0b74c9aa ("usb: dwc3: ep0: Fail
enqueue() when racing with vbus_sess disconnect") added a check
to prevent queuing on ep0 if vbus_active is unset. However on
some configurations if dwc3 is configured as peripheral-only, this
flag is not set. In those cases, simply set vbus_active to true.

Change-Id: Ica633cb9f0baefb779a516c3a32a6b92f90ced24
Fixes: 0b74c9aa ("usb: dwc3: ep0: Fail enqueue() when racing with vbus_sess disconnect")
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>