dd: code shrink

dd: code shrink

function                                             old     new   delta
write_and_stats                                       78      99     +21
dd_main                                             1496    1487      -9
full_write_or_warn                                    42       -     -42
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/1 up/down: 21/-51)            Total: -30 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>