usb: gadget: aspeed: fixup usb1 device descriptor at init time

This patch moves patch-usb1-dev-desc logic from get-descriptor handler
to "ast_vhub_fixup_usb1_dev_desc" function so the code is executed only
once (at vhub initial time).

Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>