Fix warning:

drivers/macintosh/via-pmu-backlight.c: In function ‘pmu_backlight_init’:
drivers/macintosh/via-pmu-backlight.c:140:13: warning: old-style function definition [-Wold-style-definition]
 void __init pmu_backlight_init()
             ^~~~~~~~~~~~~~~~~~
Signed-off-by: NMathieu Malaterre <malat@debian.org>
Acked-by: NDaniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>