staging: iio: tsl2583: moved code block inside else statement

The check for ch1lux > ch0lux inside tsl2583_get_lux is only valid if
the ratio is not equal to zero. Move the code block inside the else
statement. This does away with the need to initialize the variables to
zero.

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