iio: adc: ad7768-1: Remove logically dead code

iio: adc: ad7768-1: Remove logically dead code

The clamp macro returns a value within the specified range.

In ad7768_set_freq(), the value returned from clamp() is checked against
zero, which is not possible since the value would always be between
50 and 1024000.

Removed the 'if' check.

This issue was reported by static coverity analyser as logically
dead code.

Signed-off-by: Chandra Mohan Sundar <chandramohan.explore@gmail.com>
Link: https://patch.msgid.link/20250816133757.98624-1-chandramohan.explore@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>