macintosh/via-pmu: Fix build warning

Now that __fake_sleep is static, we get a warning about it being unused
in some configurations:

  drivers/macintosh/via-pmu.c:190:12: warning: '__fake_sleep' defined but not used
    190 | static int __fake_sleep;

Move it inside the ifdef where it's used to avoid the warning.

Fixes: 95d14392 ("macintosh/via-pmu: Make some symbols static")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210416114139.772236-1-mpe@ellerman.id.au