usb: dwc3: gadget: Set speed only up to the max supported

The setting of the device speed should be limited by the device's
maximum_speed. Check and prevent the driver from attempting to configure
higher than the maximum_speed.

Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/4fae4a9ebb60464d64d8b8f6fdfc2777a2206a69.1611106162.git.Thinh.Nguyen@synopsys.com


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