firmware: exynos-acpm: fix PMIC returned errno

firmware: exynos-acpm: fix PMIC returned errno

ACPM PMIC command handlers returned a u8 value when they should
have returned either zero or negative error codes.
Translate the APM PMIC errno to linux errno.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/linux-input/aElHlTApXj-W_o1r@stanley.mountain/
Fixes: a88927b534ba ("firmware: add Exynos ACPM protocol driver")
Cc: stable@vger.kernel.org
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>