Fix interpretation of the pmic_mpp_read() return code,
negative value means an error.
Signed-off-by: NIvan T. Ivanov <ivan.ivanov@linaro.org>
Reviewed-by: NBjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>