MFC r331333: Fix kernel memory disclosure in drm_infobufs

MFC r331333: Fix kernel memory disclosure in drm_infobufs

drm_infobufs() has a structure on the stack, fills it out and copies it
to userland.  There are 2 elements in the struct that are not filled out
and left uninitialized.  This will leak uninitialized kernel stack data
to userland.

Submitted by:	Domagoj Stolfa <ds815@cam.ac.uk>
Reported by:	Ilja Van Sprundel <ivansprundel@ioactive.com>
Security:	Kernel memory disclosure (798)

git-svn-id: svn://svn.freebsd.org/base/stable/10@331412 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f