genirq/proc: Return proper error code when irq_set_affinity() fails

genirq/proc: Return proper error code when irq_set_affinity() fails

write_irq_affinity() returns the number of written bytes, which means
success, unconditionally whether the actual irq_set_affinity() call
succeeded or not.

Add proper error handling and pass the error code returned from
irq_set_affinity() back to user space in case of failure.

[ tglx: Fixed coding style and massaged changelog ]

Signed-off-by: Wen Yang <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Jiang Biao <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]