buffer: Don't call va_end() twice

This is handled in the cleanup.

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
(cherry picked from commit 2ae2baf9ca)

src/buffer.c

@@ -1108,7 +1108,6 @@ int ssh_buffer_unpack_va(struct ssh_buffer_struct *buffer,
     for (p = format, count = 0; *p != '\0'; p++, count++) {
         /* Invalid number of arguments passed */
         if (argc != -1 && count > argc) {
-            va_end(ap_copy);
             rc = SSH_ERROR;
             goto cleanup;
         }