vtls: fix typo in schannel_verify.c

occurence -> occurrence

Closes #7566

lib/vtls/schannel_verify.c

@@ -80,7 +80,7 @@ static int is_cr_or_lf(char c)
 /* Search the substring needle,needlelen into string haystack,haystacklen
  * Strings don't need to be terminated by a '\0'.
  * Similar of OSX/Linux memmem (not available on Visual Studio).
- * Return position of beginning of first occurence or NULL if not found
+ * Return position of beginning of first occurrence or NULL if not found
  */
 static const char *c_memmem(const void *haystack, size_t haystacklen,
                             const void *needle, size_t needlelen)