ARM: dts: stihxxx-b2120: fix polarity of reset line of tsin0 port

According to c8sectpfe driver code we first drive reset line low and
then high to reset the port, therefore the reset line is supposed to
be annotated as "active low". This will be important when we convert
the driver to gpiod API.

Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>