regulator: wm8350: fix missing increment of loop index i

It seems that the loop index i is not being incremented and hence
potentially the while loop could spin forever. Fortunately with the
data being used this does not appear to happen at the moment.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>