[subset] fix up hb_subset_preprocess api comment.

docs/harfbuzz-sections.txt

@@ -783,6 +783,7 @@ hb_subset_plan_execute_or_fail
 hb_subset_plan_unicode_to_old_glyph_mapping
 hb_subset_plan_new_to_old_glyph_mapping
 hb_subset_plan_old_to_new_glyph_mapping
+hb_subset_preprocess
 hb_subset_flags_t
 hb_subset_input_t
 hb_subset_sets_t
@@ -791,7 +792,6 @@ hb_subset_plan_t
 hb_link_t
 hb_object_t
 hb_subset_repack_or_fail
-hb_subset_preprocess
 hb_subset_input_pin_axis_location
 hb_subset_input_pin_axis_to_default
 hb_subset_input_override_name_table

docs/subset-preprocessing.md

@@ -21,7 +21,7 @@ hb_face_t* subset = hb_subset_or_fail (preprocessed, subset_input);
    original face. The preprocessor does not change the functionality of the subsetter, just speeds
    things up.
 
-*  The preprocessing operation may take longer then the time it takes to produce a subset from the
+*  The preprocessing operation may take longer than the time it takes to produce a subset from the
    source font. Thus the main performance gains are made when a preprocessed face is reused for
    multiple subsetting operations.
 

src/hb-subset-input.cc

@@ -449,12 +449,12 @@ hb_subset_input_pin_axis_location (hb_subset_input_t  *input,
 #endif
 
 /**
- * hb_subset_preprocess
- * @input: a #hb_face_t object.
+ * hb_subset_preprocess:
+ * @source: a #hb_face_t object.
  *
  * Preprocesses the face and attaches data that will be needed by the
  * subsetter. Future subsetting operations can then use the precomputed data
- * to speed up the subsetting operation. Returns a new hb_face_t*.
+ * to speed up the subsetting operation.
  *
  * See docs/subset-preprocessing.md for more information.
  *
@@ -463,6 +463,8 @@ hb_subset_input_pin_axis_location (hb_subset_input_t  *input,
  * owned by the source face you will need to ensure that memory lives
  * as long as the returned hb_face_t*.
  *
+ * Returns: a new hb_face_t*.
+ *
  * Since: REPLACEME
  **/