power: supply: max77705: Fix workqueue error handling in probe

The create_singlethread_workqueue() doesn't return error pointers, it
returns NULL.  Also cleanup the workqueue on the error paths.

Fixes: a6a494c8 ("power: supply: max77705: Add charger driver for Maxim 77705")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/547656e3-4a5f-4f2e-802b-4edcb7c576b0@stanley.mountain


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>