tools/power turbostat: remove blank lines

When the user reuests to collect and show columns
that are not present on every row (eg. for every CPU)
turbostat still prints an (empty) line for every CPU.
Update so no blank lines are printed.

old:
	# turbostat --quiet --show Pkg%pc6
	Pkg%pc6
	9.12
	9.12

	Pkg%pc6
	9.12
	9.12

new:
	# turbostat --quiet --show Pkg%pc6
	Pkg%pc6
	9.12
	9.12
	Pkg%pc6
	9.12
	9.12

Reported-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>