This is a clean-up patch which removes the own pseudo-random numbers generator
from the speed- and stress-tests and makes them use the 'random32()' generator
instead.

[dwmw2: Merge later fix for negative offsets]
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>