ARM: s3c24xx: bast: avoid irq_desc array usage

Once we move to sparse irqs, the irq_desc[] array is no
longer accessible, so replace the two uses in bast-irq.c.
The first one can use irq_to_desc(), the second one seems
completely unneeded as we already have a pointer to the
correct descriptor.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200806182059.2431-32-krzk@kernel.org


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