clk: imx8mq: set correct parent for usb ctrl clocks

Per latest imx8mq datasheet of CCM, the parent of usb1_ctrl_root_clk
and usb2_ctrl_root_clk is usb_bus.

Signed-off-by: Li Jun <jun.li@nxp.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>