iio: temperature: ltc2983: remove redundant comparison to bool

Remove redundant comparison to a boolean variable.

Fixes coccinelle warning:
drivers/iio/temperature//ltc2983.c:393:20-32: WARNING: Comparison to bool
drivers/iio/temperature//ltc2983.c:394:20-32: WARNING: Comparison to bool

Signed-off-by: Rohit Sarkar <rohitsarkar5398@gmail.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>