staging:iio:meter: Add name to function definition arguments

This patch fixes the checkpatch.pl warning:

drivers/staging/iio/meter/ade7854.h:157: WARNING: function definition
argument 'struct device *' should also have an identifier name...

This commit adds arguments names to the signature declared in the
ade7854_state struct. For consistency reason, It also renames all
arguments in function definitions.

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>