tools:iio:iio_utils: free scan_el_dir on exit

In the error path, the string scan_el_dir got freed, while it was missing when
build_channel_array() finished without errors.

Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

tools/iio/iio_utils.c

@@ -403,6 +403,7 @@ int build_channel_array(const char *device_dir,
 	}
 
 	closedir(dp);
+	free(scan_el_dir);
 	/* reorder so that the array is in index order */
 	bsort_channel_array_by_index(ci_array, *counter);