iio:accel:Switch hardcoded function name with a reference to __func__ making the code more maintainable

It fixes the following checkpatch.pl warning:

WARNING: Prefer using '"%s...", __func__' to using function's name, in a
string
Signed-off-by: Mohan Kumar <mohankumar718@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>