staging: iio: tsl2583: check for error code from i2c_smbus_read_byte()

taos_i2c_read() and taos_als_calibrate() does not check to see if the
value returned by i2c_smbus_read_byte() was an error code. This patch
adds the appropriate error handling.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>