ARM: dts: stm32: change joystick pinctrl definition on stm32mp157c-ev1

Pins used for joystick are all configured as input. "push-pull" is not a
valid setting for an input pin.

Fixes: a502b343 ("pinctrl: stmfx: update pinconf settings")
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>