usb: mtu3: fix the wrong HS mult value

usb_endpoint_maxp() returns actual max packet size, @mult will
always be zero, fix it by using usb_endpoint_maxp_mult() instead
to get mult.

Fixes: 4d79e042 ("usb: mtu3: add support for usb3.1 IP")
Cc: stable@vger.kernel.org
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1628836253-7432-3-git-send-email-chunfeng.yun@mediatek.com


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