arm64: dt: imx93: tqma9352-mba93xxla: Fix LPUART2 pad config

LPUART2_RTS# has an external pull-down, so do not enable the internal
pull-up at the same time, use a pull-down instead.

Fixes: c982ecfa ("arm64: dts: freescale: add initial device tree for MBa93xxLA SBC board")
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>