staging: iio: remove unnecessary parentheses

Clean up checkpatch warning:
CHECK: Unnecessary parentheses around 'st->devid != ID_AD7195'

Signed-off-by: Ji-Hun Kim <jihuun.k@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>