usb: xhci-mtk: use @sch_tt to check whether need do TT schedule

usb: xhci-mtk: use @sch_tt to check whether need do TT schedule

[ Upstream commit 4a56adf4fafbc41ceffce0c3f385f59d4fc3c16a ]

It's clearer to use @sch_tt to check whether need do TT schedule,
no function is changed.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/324a76782ccaf857a8f01f67aee435e8ec7d0e28.1615170625.git.chunfeng.yun@mediatek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 548011957d1d ("usb: xhci-mtk: relax TT periodic bandwidth allocation")
Signed-off-by: Sasha Levin <sashal@kernel.org>