update lib/ymodem.c

Signed-off-by: surenyi <surenyi82@163.com>

lib/ymodem.c

@@ -334,14 +334,14 @@ retry:
 
         /* eot */
         if (pkt_size == 0) {
-            if (rx->eot == 1) {
+            switch (rx->eot) {
+                case 1:
                     put_byte(uart, NAK);
-                continue;
+                    break;
-            }
+                case 2:
-
-            if (rx->eot == 2) {
                     put_byte(uart, ACK);
                     put_byte(uart, WANTCRC);
+                    break;
             }
         }
     }