[ARM] gic: Fix gic cascade irq handling

No need for the cascade irq function to have a "fastcall" annotation.
Fix the range checking for valid IRQ numbers - comparing the value
returned by the GIC with NR_IRQS is meaningless since we translate
the GIC irq number to a Linux IRQ number afterwards.

Check the GIC returned IRQ number is within limits first, then add
the IRQ offset, and only then compare with NR_IRQS.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>