iio: temperature: ltc2983: Fix reinit_completion() called after conversion start

iio: temperature: ltc2983: Fix reinit_completion() called after conversion start

reinit_completion() was called after regmap_write() initiated the hardware
conversion, creating a race window where the interrupt could fire and call
complete() before reinit_completion() reset the completion.

Move reinit_completion() before the regmap_write() to close the race.
ltc2983_eeprom_cmd() already does it in the correct order.

Fixes: f110f3188e56 ("iio: temperature: Add support for LTC2983")
Signed-off-by: Liviu Stan <liviu.stan@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>