random: Use unsigned long for seed

v2: Remove unrelated change in main()

This is more consistent with the rest, and avoids potential undefined
behavior (signed overflow) ind drmRandom()

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Ian Romanick <idr@freedesktop.org>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>