usb: xhci-mtk: use xhci_dbg() to print log

Use xhci_dbg() to print log instead of xhci_err() due to it's not
error log.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20210923071447.15688-1-chunfeng.yun@mediatek.com


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