Re-factor proc_pid_cmdline() to use get_cmdline() helper
from mm.h.
Acked-by: David Rientjes <rientjes@google.com> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> Acked-by: Richard Guy Briggs <rgb@redhat.com> Signed-off-by: William Roberts <wroberts@tresys.com> Acked-by: Richard Guy Briggs <rgb@redhat.com> Signed-off-by: Eric Paris <eparis@redhat.com>