arm64: dts: imx8mm-venice: fix spi2 pin configuration

Due to what looks like a copy-paste error, the ECSPI2_MISO pad is not
muxed for SPI mode and causes reads from a slave-device connected to the
SPI header to always return zero.

Configure the ECSPI2_MISO pad for SPI mode on the gw71xx, gw72xx and
gw73xx families of boards that got this wrong.

Fixes: 6f30b27c ("arm64: dts: imx8mm: Add Gateworks i.MX 8M Mini Development Kits")
Cc: stable@vger.kernel.org      # 5.12
Cc: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>