mfd: stmpe: Only disable the regulators if they are enabled

In stmpe_probe(), if some regulator_enable() calls fail, probing continues
and there is only a dev_warn().

So, if stmpe_probe() is called the regulator may not be enabled. It is
cleaner to test it before calling regulator_disable() in the remove
function.

Fixes: 9c9e3214 ("mfd: stmpe: add optional regulators")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/8de3aaf297931d655b9ad6aed548f4de8b85425a.1686998575.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Lee Jones <lee@kernel.org>