USB: dummy-hcd: fix power budget for SuperSpeed mode

The power budget for SuperSpeed mode should be 900 mA
according to USB specification, so set the power budget
to 900mA for dummy_start_ss which is only used for
SuperSpeed mode.

If the max power consumption of SuperSpeed device is
larger than 500 mA, insufficient available bus power
error happens in usb_choose_configuration function
when the device connects to dummy hcd.

Signed-off-by: Jacky Cao <Jacky.Cao@sony.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/16EA1F625E922C43B00B9D82250220500871CDE5@APYOKXMS108.ap.sony.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>