arm64: dts: imx8: change the spi-nor tx

Before commit 0e30f472 ("mtd: spi-nor: add support for DTR protocol"),
for all PP command, it only support 1-1-1 mode, no matter the tx setting
in dts. But after the upper commit, the logic change. It will choose
the best mode(fastest mode) which flash device and spi-nor host controller
both support.

qspi and fspi host controller do not support read 1-4-4 mode. so need to
set the tx to 1, let the common code finally select read 1-1-4 mode.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Fixes: 0e30f472 ("mtd: spi-nor: add support for DTR protocol")
Signed-off-by: Shawn Guo <shawnguo@kernel.org>