printer CHANGE return LY_ERR in a standard way from ly_write_skipped()

Returning number of written bytes does not make sense in this case.
diff --git a/src/printer_internal.h b/src/printer_internal.h
index d32d1ad..9c926fb 100644
--- a/src/printer_internal.h
+++ b/src/printer_internal.h
@@ -171,10 +171,9 @@
  * @param[in] buf Memory buffer with the data to print.
  * @param[in] len Length of the data to print in the @p buf. Not that the length must correspond
  * to the len value specified in the corresponding ly_write_skip() call.
- * @return The number of bytes prepared for write. The number of the printed bytes is updated in lyout::printed
- * only in case the data are really written into the output.
- * @return Negative value in case of error, absolute value of the return code maps to LY_ERR value.
+ * @return LY_SUCCESS on success.
+ * @return LY_ERR value in case of error.
  */
-ssize_t ly_write_skipped(struct ly_out *out, size_t position, const char *buf, size_t len);
+LY_ERR ly_write_skipped(struct ly_out *out, size_t position, const char *buf, size_t len);
 
 #endif /* LY_PRINTER_INTERNAL_H_ */