staging: iio: meter: replace ternary operator by if condition

Replace ternary operator by simple if based evaluation of the return
value. Issue identified using coccicheck.

Signed-off-by: Deepak R Varma <drv@mailo.com>
Link: https://lore.kernel.org/r/Y3CAdCa17WdWDYUa@qemulion
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>