staging: iio: tsl2583: remove redundant power off sequence in taos_chip_on()

taos_chip_on() explicitly turns the sensor power on and then writes the
8 registers that are stored in taos_config. The first register in
taos_config is the CONTROL register and the configuration is set to
turn the power off. The existing state sequence in taos_chip_on() is:

- Turn device power on
- Turn device power off (via taos_config)
- Configure other 7 registers (via taos_config)
- Turn device power on, enable ADC

This patch changes the code so that the device is not powered off via
taos_config.

Verified that the driver still functions correctly using a TSL2581
hooked up to a Raspberry Pi 2.

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