usb: dwc3: gadget: Preserve UDC max speed setting

The USB gadget/UDC driver can restrict the DWC3 controller speed using
dwc3_gadget_set_speed().  Store this setting into a variable, in order for
this setting to persist across controller resets due to runtime PM.

Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
Link: https://lore.kernel.org/r/1609283136-22140-3-git-send-email-wcheng@codeaurora.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>