usb: dwc3: otg: don't clear event buffers when changing to Host mode from Device...

usb: dwc3: otg: don't clear event buffers when changing to Host mode from Device mode

Clearing event buffers when changing from Device mode -> Host mode
may require allocating event buffers again during role swap from
Host mode -> Device mode. Changing the event buffers at runtime are
not triggering events in device mode and also the role swap can happen
at any time. So, better not to clear the event buffers during role
swap instead reuse the previously allocated event buffers.
This patch does the same.

Signed-off-by: Anurag Kumar Vulisha <anuragku@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>