powerpc/8xx: fix mpc8xx_get_irq() return on no irq

[Michael Ellerman]

On Fri, 2017-03-10 at 10:37:01 UTC, Christophe Leroy wrote:
> IRQ 0 is a valid HW interrupt. So get_irq() shall return 0 when
> there is no irq, instead of returning irq_linear_revmap(... ,0)
> 
> Fixes: f2a0bd3753dad ("[POWERPC] 8xx: powerpc port of core CPM PIC")
> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/3c29b6038828c1f4c9ecbfec14d4fc

cheers