tools/power turbostat: fix parameter passing for forked command

turbostat supports forked command when sampling cpu state. However,
the forked command is not allowed to be executed with options, otherwise
turbostat might regard these options as invalid turbostat options.

For example:

./turbostat stress -c 4 -t 10
./turbostat: unrecognized option '-t'

Reported-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>