genirq/proc: Change the return value for set affinity permission error

Currently, when the affinity of an irq cannot be set due to lack of
permission, the write_irq_affinity() returns the error code -EIO.

Change the return value to -EPERM as that reflects the cause of error
correctly.

Signed-off-by: Jeff Xie <jeff.xie@linux.dev>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240826145805.5938-1-jeff.xie@linux.dev