iio: adc: mcp3911: avoid ambiguity parameters in macros

Name macro parameters after what they represent instead of 'x'
and make sure the evaluation of that will have no side effects.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Link: https://lore.kernel.org/r/20230822192259.1125792-6-marcus.folkesson@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>