vim-patch:8.1.0528: various typos in comments

Problem:    Various typos in comments.
Solution:   Fix the typos.
c4568ab37e

src/nvim/search.c

@@ -310,7 +310,7 @@ void free_search_patterns(void)
 /// Save and restore the search pattern for incremental highlight search
 /// feature.
 ///
-/// It's similar but different from save_search_patterns() and
+/// It's similar to but different from save_search_patterns() and
 /// restore_search_patterns(), because the search pattern must be restored when
 /// cancelling incremental searching even if it's called inside user functions.
 void save_last_search_pattern(void)

src/nvim/spell.c

@@ -2294,7 +2294,7 @@ static void use_midword(slang_T *lp, win_T *wp)
 }
 
 // Find the region "region[2]" in "rp" (points to "sl_regions").
-// Each region is simply stored as the two characters of it's name.
+// Each region is simply stored as the two characters of its name.
 // Returns the index if found (first is 0), REGION_ALL if not found.
 static int find_region(char_u *rp, char_u *region)
 {

src/nvim/spellfile.c

@@ -3227,7 +3227,7 @@ static int get_pfxlist(afffile_T *affile, char_u *afflist, char_u *store_afflist
     prevp = p;
     if (get_affitem(affile->af_flagtype, &p) != 0) {
       // A flag is a postponed prefix flag if it appears in "af_pref"
-      // and it's ID is not zero.
+      // and its ID is not zero.
       STRLCPY(key, prevp, p - prevp + 1);
       hi = hash_find(&affile->af_pref, key);
       if (!HASHITEM_EMPTY(hi)) {