cpupowerutils: bench - Fix cpu online check

cpupower_is_cpu_online was incorrectly checking for 0. This patch fixes
this by checking for 1 when the cpu is online.

Signed-off-by: Abhishek Goel <huntbag@linux.vnet.ibm.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>