Staging: iio: meter: Prefer using the BIT macro

This patch replaces bit shifting on 1 with the BIT(x) macro

This was done with coccinelle:
@@ int g; @@

-(1 << g)
+BIT(g)

Signed-off-by: Shraddha Barke <shraddha.6596@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>