ASoC: max98388: fix error code in probe()

This seems like a copy and paste bug.  Return the correct variable.
It should be "ret" instead of PTR_ERR(max98388->regmap).

Fixes: 6a8e1d46 ("ASoC: max98388: add amplifier driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/d44c8388-b12b-4045-95de-0d4bc7b428ac@moroto.mountain


Signed-off-by: Mark Brown <broonie@kernel.org>