regulator: stw481x-vmmc: fix ages old enable error

The regulator has never been properly enabled, it has been
dormant all the time. It's strange that MMC was working
at all, but it likely worked by the signals going through
the levelshifter and reaching the card anyways.

Fixes: 3615a34e ("regulator: add STw481x VMMC driver")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org