usb: mtu3: remove repeated setting of speed

mtu3_gadget_start() will set speed, no need set it again in
mtu3_gadget_set_speed(), just save the desired speed.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1622182260-23767-2-git-send-email-chunfeng.yun@mediatek.com


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