In grub-core/osdep/unix/getroot.c, Coverity spotted redundant code where the
double pointer os_dev was being set to 0 and then being overwritten later
without being used. Since this is unnecessary, we can remove the code that
sets os_dev to 0.
Fixes: CID 428875 Signed-off-by: Alec Brown <alec.r.brown@oracle.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>