busybox

dd: fix bug where we assume count=INT_MAX when count is unspecified;
shrink dd while at it

function                                             old     new   delta
dd_main                                             1453    1368     -85
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-85)             Total: -85 bytes
   text    data     bss     dec     hex filename
 669216    2668   13616  685500   a75bc busybox_old
 669128    2668   13616  685412   a7564 busybox_unstripped