irqchip: s3c24xx: add missing __init annotations

The s3c24xx_init_intc and s3c2412_init_irq functions are only called
at init time, and they call functions already marked __init, so they
should be marked in the same way. This was reported as

WARNING: vmlinux.o(.text+0x19e0b4): Section mismatch in reference from the function s3c2412_init_irq() to the function .init.text:s3c24xx_init_intc.constprop.8()
The function s3c2412_init_irq() references
the function __init s3c24xx_init_intc.constprop.8().
This is often because s3c2412_init_irq lacks a __init
annotation or the annotation of s3c24xx_init_intc.constprop.8 is wrong.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Cc: Kukjin Kim <kgene.kim@samsung.com>