powertop: fix segfault on non-SMP processors

Non-SMP processors do not have the 'processor' line, so we need
to default to 0.

Change-Id: I38af003e62d87e25100c19acaf730fe4730b2a18
Merge pull request #1 from CyanogenMod/cm-11.0

powertop: fix segfault on non-SMP processors