UPSTREAM: drm/virtio: Use IDAs more efficiently

0-based IDAs are more efficient than any other base.  Convert the
1-based IDAs to be 0-based.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20181030165352.13065-2-willy@infradead.org


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 2ae7f165c0b022a8ed1732f8ab2c11b2c173146e)
Signed-off-by: Greg Hartman <ghartman@google.com>
BUG: 139386237
Change-Id: I163fea3a31358bbaa478c1ce49b42de413ddc9d5