iio: pressure: hsc030pa: Improve i2c_transfer return value handling

iio: pressure: hsc030pa: Improve i2c_transfer return value handling

The i2c_transfer() function returns the number of messages
successfully transferred. The function sends 1 message but checks
for ret == 2, which can never be true.

In practice this has no impact since the caller checks ret < 0,
and the erroneous return value of 1 is not treated as an error.

Improve the return value handling to properly distinguish between
I2C errors and unexpected transfer counts.

Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Tested-by: Petre Rodan <petre.rodan@subdimension.ro>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>