staging: iio: tsl2x7x: remove tsl2x7x_i2c_read()

tsl2x7x_i2c_read() would call i2c_smbus_write_byte() and
i2c_smbus_read_byte(). These two i2c functions can be replaced with a
single call to i2c_smbus_read_byte_data(). This patch removes the
tsl2x7x_i2c_read() function and replaces all occurrences with a call to
i2c_smbus_read_byte_data().

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