regulator: 88pm800: Fix checking whether num_regulator is valid

The code to check whether num_regulator is valid is wrong because it should
iterate all array entries rather than break from the for loop if
pdata->regulators[i] is NULL.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>