If a GPIO we are trying to use is not available and we are deferring
the probe, don't output an error message.
This seems to have been the intent of commit 05c74778
("i2c: gpio: Add support for named gpios in DT") but the error was
still output due to not checking the updated 'retdesc'.

Fixes: 05c74778 ("i2c: gpio: Add support for named gpios in DT")
Signed-off-by: Hamish Martin <hamish.martin@alliedtelesis.co.nz>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>