hwmon: (lm90) Make code more readable

Clean up the code to make it more readable:
* Remove reg_ and new_ prefixes from variable names, they made the
  names longer, causing extra line breaks, while not adding much
  value.
* Introduce struct device dev* = &client->dev in two functions, to
  avoid repeating client->dev everywhere in these functions.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>