when used in a VIEW.

The problem was that wrong function (create_tmp_from_item())
was used to create a temporary field for Item_func_sp.

The fix is to use create_tmp_from_field().


mysql-test/r/sp.result:
  Update result file.
mysql-test/t/sp.test:
  Add a test case for BUG#20550.
sql/item_func.h:
  Add a getter for Item_func_sp::sp_result_field.
sql/sql_select.cc:
  Use create_tmp_from_field() to create a temporary field
  for Item_func_sp.