regulator: Fix display of null constraints for regulators

regulator: Fix display of null constraints for regulators

commit 973e9a2795b3b41d8408a0bb6f87b783c5efc88a upstream.

If the regulator constraints are empty and there is no voltage
reported then nothing will be added to the text displayed for the
constraints, leading to random stack data being printed. This is
unlikely to happen for practical regulators since most will at
least report a voltage but should still be fixed.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>