irqchip/s3c24xx: Remove unneeded comparison of unsigned long to 0

irq_data->hwirq is unsigned long.  This fixes GCC warning:

    drivers/irqchip/irq-s3c24xx.c: In function 's3c_irqext0_type':
    drivers/irqchip/irq-s3c24xx.c:253:19: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
      if ((data->hwirq >= 0) && (data->hwirq <= 3)) {
                       ^~

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>