iio: core: Replace iio_sysfs_match_string_with_gaps() by __sysfs_match_string()

None of the current users is using gaps in the list of the items.
No need to have a specific function for that, just replace it by
library available __sysfs_match_string().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230118074828.66155-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>