staging: iio: ad7152: Use BIT() macro for left shifting 1

Replace left shifting on 1 with the BIT(x) macro as suggested by
checkpatch.pl.

Signed-off-by: sayli karnik <karniksayli1995@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>