iio:potentiostat:lmp91000: reduce line width and remove blank line

Break the line 258 in order fit the line width on 80 characters. Remove
the blank line 279, as the line before is also a blank line. Solve these
checkpath.el WARNING and CHECK:

- lmp91000.c:258: WARNING: line over 80 characters
- lmp91000.c:279: CHECK: Please don't use multiple blank lines

Signed-off-by: Lucas Oshiro <lucasseikioshiro@gmail.com>
Signed-off-by: Anderson Reis <andersonreisrosa@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>