usb: composite: Fix max packet size for USB3.0

usb: composite: Fix max packet size for USB3.0

For USB3.0, the max packetsize for GET_DESCRIPTOR should be
sent as exponent value for 2. This means for 512, max packet
size should be filled with 9(2^9=512). Also, fill the USB
version field with 3.0 if speed is negotiated to Superspeed.
This fixes the issue of DFU gadget download failure with
superspeed. Without this patch, the max packet size is
overflowed to zero as the bMaxPacketsize is of u8 and hence
host is not able to detect this device.

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>