MIPS: loongson64: Drop call to irq_cpu_offline()

Also loongson64 calls irq_cpu_offline(), none of its interrupt
controllers implement the .irq_cpu_offline callback.

It is thus obvious that this call only serves the dubious purpose
of wasting precious CPU cycles by iterating over all interrupts.

Get rid of the call altogether.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20211021170414.3341522-2-maz@kernel.org