The SAI2_TXC pin is left unconnected per the imx8mp-debix-model-a
schematics:

https://debix.io/Uploads/Temp/file/20230331/DEBIX%20Model%20A%20Schematics.pdf

Also, the RTS5411E USB hub chip does not have a reset pin.

Remove this pin description to properly describe the hardware.

This also fixes the following schema warning:

hub@1: 'reset-gpios' does not match any of the regexes: 'pinctrl-[0-9]+'
from schema $id: http://devicetree.org/schemas/usb/realtek,rts5411.yaml#

Fixes: 0253e1cb ("arm64: dts: imx8mp-debix: add USB host support")
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>