irqchip/stm32: Don't set rising configuration registers at init

The rising configuration status register (rtsr) is not banked.
As it is shared with the co-processor, it should not be written at probe
time, else the co-processor configuration will be lost.

Fixes: f9fc1745 ("irqchip/stm32: Add host and driver data structures")
Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>