mfd: tps6594: Fix an error code in probe()

These error paths accidentally return success when they should return
-EINVAL.

Fixes: 325bec71 ("mfd: tps6594: Add driver for TI TPS6594 PMIC")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/49f7cd8f-f7eb-40f1-91e8-291620c684df@kili.mountain


Signed-off-by: Lee Jones <lee@kernel.org>