nanocoap_sock: use correct error code in nanocoap_get_blockwise_url_to_buf()

It should return -ENOBUFS like the other nanocoap_…() functions, not -1

sys/include/net/nanocoap_sock.h

@@ -308,8 +308,9 @@ int nanocoap_get_blockwise_url(const char *url,
  * @param[in]   buf        Target buffer
  * @param[in]   len        Target buffer length
  *
+ * @returns     <0 on error
  * @returns     -EINVAL    if an invalid url is provided
- * @returns     -1         if failed to fetch the url content
+ * @returns     -ENOBUFS   if the provided buffer was too small
  * @returns     size of the response payload on success
  */
 ssize_t nanocoap_get_blockwise_url_to_buf(const char *url,

sys/net/application_layer/nanocoap/sock.c

@@ -568,7 +568,7 @@ static int _2buf(void *arg, size_t offset, uint8_t *buf, size_t len, int more)
     _buf_t *dst = arg;
 
     if (offset + len > dst->len) {
-        return -1;
+        return -ENOBUFS;
     }
 
     memcpy(dst->ptr + offset, buf, len);