x509asn1: use FALLTHROUGH

... as no other comments are accepted since 014ed7c22f

lib/x509asn1.c

@@ -302,10 +302,10 @@ utf8asn1str(char **to, int type, const char *from, const char *end)
       case 4:
         wc = (wc << 8) | *(const unsigned char *) from++;
         wc = (wc << 8) | *(const unsigned char *) from++;
-        /* fallthrough */
+        /* FALLTHROUGH */
       case 2:
         wc = (wc << 8) | *(const unsigned char *) from++;
-        /* fallthrough */
+        /* FALLTHROUGH */
       default: /* case 1: */
         wc = (wc << 8) | *(const unsigned char *) from++;
       }