Fix some typos in comments and strings

Most of them were found and fixed by codespell.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

rewritten from github.com/moby/moby 2eee613326fb59fd168849618d14a9054a40f9f5

frontend/dockerfile/parser/line_parsers.go

@@ -71,7 +71,7 @@ func parseWords(rest string) []string {
 			if unicode.IsSpace(ch) { // skip spaces
 				continue
 			}
-			phase = inWord // found it, fall thru
+			phase = inWord // found it, fall through
 		}
 		if (phase == inWord || phase == inQuote) && (pos == len(rest)) {
 			if blankOK || len(word) > 0 {

frontend/dockerfile/parser/utils.go

@@ -118,7 +118,7 @@ func extractBuilderFlags(line string) (string, []string, error) {
 				return line[pos:], words, nil
 			}
 
-			phase = inWord // found someting with "--", fall thru
+			phase = inWord // found someting with "--", fall through
 		}
 		if (phase == inWord || phase == inQuote) && (pos == len(line)) {
 			if word != "--" && (blankOK || len(word) > 0) {