sparc/of: Remove on-stack cpumask var

sparc/of: Remove on-stack cpumask var

In general it's preferable to avoid placing cpumasks on the stack, as
for large values of NR_CPUS these can consume significant amounts of
stack space and make stack overflows more likely.

@cpumask of irq_set_affinity() is read-only and free of change, drop
unneeded cpumask var.

Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Dawei Li <dawei.li@shingroup.cn>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Link: https://lore.kernel.org/r/20240424025548.3765250-4-dawei.li@shingroup.cn
Signed-off-by: Andreas Larsson <andreas@gaisler.com>