serial: max310x: Add error checking in probe()

Check if devm_i2c_new_dummy_device() fails.

Fixes: 2e1f2d9a ("serial: max310x: implement I2C support")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/aJTMPZiKqeXSE-KM@stanley.mountain


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>