Item_func_div::fix_length_and_dec_temporal() set the return data type to
integer in case of @div_precision_increment==0 for temporal input with FSP=0.
This caused Item_func_div to call int_op(), which is not implemented,
so a crash on DBUG_ASSERT(0) happened.

Fixing fix_length_and_dec_temporal() to set the result type to DECIMAL.