hwmon: (ads7871) Convert to hwmon_device_register_with_info

hwmon: (ads7871) Convert to hwmon_device_register_with_info

Convert the ads7871 driver from the legacy hwmon_device_register() to the
modern hwmon_device_register_with_info() API. This migration simplifies
the driver by using the structured hwmon_channel_info approach and
prepares the codebase for the transition to a shared DMA-safe buffer.
While at it, fix checkpatch violations.

Signed-off-by: Tabrez Ahmed <tabreztalks@gmail.com>
Link: https://lore.kernel.org/r/20260502020844.110038-3-tabreztalks@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>