UPSTREAM: drm/virtio: Handle context ID allocation errors

It is possible to run out of memory while allocating IDs.  The current
code would create a context with an invalid ID; change it to return
-ENOMEM to userspace.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20180926160031.15721-3-willy@infradead.org


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 6a37c49a94a95d4cd8ce4e7466f3bbb17e80ca64)
Signed-off-by: Greg Hartman <ghartman@google.com>
BUG: 139386237
Change-Id: I009960f3fb372875f9e0fab403e01d1148bed23d