ash: small size optimization

ash: small size optimization
function                                             old     new   delta
makejob                                              263     270      +7
setjobctl                                            328     332      +4
jobscmd                                               96      94      -2
stoppedjobs                                           53      50      -3
jobctl                                                 4       1      -3
job_warning                                            4       1      -3
forkshell                                            644     641      -3
cmdloop                                              422     409     -13
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/6 up/down: 11/-27)            Total: -16 bytes
   text    data     bss     dec     hex filename
 675392    2740   13968  692100   a8f84 busybox_old
 675380    2740   13968  692088   a8f78 busybox_unstripped