x86: PM: Make APM idle driver initialize polling state

Update the APM driver overlooked by commit 1b39e3f8 (cpuidle: Make
drivers initialize polling state) to initialize the polling state like
the other cpuidle drivers modified by that commit to prevent cpuidle
from crashing.

Fixes: 1b39e3f8

 (cpuidle: Make drivers initialize polling state)
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: 4.14+ <stable@vger.kernel.org> # 4.14+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>