When suspending to idle with the new suspend mode configuration support
we go through the suspend callbacks with a state of PM_SUSPEND_TO_IDLE
which we don't have regulator constraints for, causing an error.  Avoid
this and similar errors by treating missing constraints as a noop.
Reported-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Tested-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NMark Brown <broonie@kernel.org>