ARM: s3c24xx: spi: avoid hardcoding fiq number in driver

The IRQ_EINT0 constant is a platform detail that is
defined in mach/irqs.h and not visible to drivers once
that header is made private.

Since the same calculation already happens in s3c24xx_set_fiq,
just return the value from there.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20200806182059.2431-31-krzk@kernel.org


Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>