smtp.c: Fixed compilation warnings

smtp.c:2357 warning: adding 'size_t' (aka 'unsigned long') to a string
            does not append to the string
smtp.c:2375 warning: adding 'size_t' (aka 'unsigned long') to a string
            does not append to the string
smtp.c:2386 warning: adding 'size_t' (aka 'unsigned long') to a string
            does not append to the string

Used array index notation instead.

lib/smtp.c

@@ -2354,7 +2354,7 @@ CURLcode Curl_smtp_escape_eob(struct connectdata *conn, const ssize_t nread)
     }
     else if(smtp->eob) {
       /* A previous substring matched so output that first */
-      memcpy(&scratch[si], SMTP_EOB + eob_sent, smtp->eob - eob_sent);
+      memcpy(&scratch[si], &SMTP_EOB[eob_sent], smtp->eob - eob_sent);
       si += smtp->eob - eob_sent;
 
       /* Then compare the first byte */
@@ -2372,7 +2372,7 @@ CURLcode Curl_smtp_escape_eob(struct connectdata *conn, const ssize_t nread)
     /* Do we have a match for CRLF. as per RFC-5321, sect. 4.5.2 */
     if(SMTP_EOB_FIND_LEN == smtp->eob) {
       /* Copy the replacement data to the target buffer */
-      memcpy(&scratch[si], SMTP_EOB_REPL + eob_sent,
+      memcpy(&scratch[si], &SMTP_EOB_REPL[eob_sent],
              SMTP_EOB_REPL_LEN - eob_sent);
       si += SMTP_EOB_REPL_LEN - eob_sent;
       smtp->eob = 0;
@@ -2384,7 +2384,7 @@ CURLcode Curl_smtp_escape_eob(struct connectdata *conn, const ssize_t nread)
 
   if(smtp->eob - eob_sent) {
     /* A substring matched before processing ended so output that now */
-    memcpy(&scratch[si], SMTP_EOB + eob_sent, smtp->eob - eob_sent);
+    memcpy(&scratch[si], &SMTP_EOB[eob_sent], smtp->eob - eob_sent);
     si += smtp->eob - eob_sent;
   }