Use a constant size for the copy

1 job for fix-pocl-error-rotation in 3 minutes and 31 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Test
failed #9109
tox_tests

00:03:31

 
Name Stage Failure
failed
tox_tests Test There is an unknown failure, please try again
                [8] %.lr.ph.prol.i {35,38}
[9] %.lr.ph.preheader.split.loopexit.i {36,37}
[5] %_Z21async_work_group_copyPU7CLlocalfPKU8CLglobalfm9ocl_event.exit {42,45}
[6] %._crit_edge10 {43,44}
ERROR: InvocationError: '/builds/grp-svergun/galumph/.tox/py35/bin/pytest -sv'
___________________________________ summary ____________________________________
ERROR: py27: commands failed
ERROR: py35: commands failed
ERROR: Job failed: exit code 1