ARM: s3c: irq-s3c24xx: Fix return value check for s3c24xx_init_intc()

The s3c24xx_init_intc() returns an error pointer upon failure, not NULL.
let's add an error pointer check in s3c24xx_handle_irq.

s3c_intc[0] is not NULL or ERR, we can simplify the code.

Fixes: 1f629b7a ("ARM: S3C24XX: transform irq handling into a declarative form")
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Link: https://lore.kernel.org/r/20210901123557.1043953-1-liu.yun@linux.dev


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>