genirq: fix the affinity setting in setup_irq

The affinity setting in setup irq is called before the NO_BALANCING
flag is checked and might therefore override affinity settings from the
calling code with the default setting.

Move the NO_BALANCING flag check before the call to the affinity
setting.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>