staging: iio: tsl2583: unify function and variable prefix to tsl2583_

Some functions and variables were prefixed with either taos, tsl258x,
taos2583, or tsl2583. Change everything to use the tsl2583 prefix since
that is the name of the .c file. The taos_settings member inside the
taos_settings struct was renamed to als_settings.

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