irqchip/stm32-exti: Fix warning on initialized field overwritten

While compiling with W=1, both gcc and clang complain about a
tricky way to initialize an array by filling it with a non-zero
value and then overrride some of the array elements.
In this case the override is intentional, so just disable the
specific warning for only this part of the code.

Note: the flag "-Woverride-init" is recognized by both compilers,
but the warning msg from clang reports "-Winitializer-overrides".
The doc of clang clarifies that the two flags are synonyms, so use
here only the flag name common on both compilers.

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Fixes: c2974933 ("irqchip/stm32-exti: Simplify irq description table")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230601155614.34490-1-antonio.borneo@foss.st.com