simple-dmabuf-drm: use appropriately sized buffer (freedreno)

Use stride instead of width for buffer calculation.

[Derek Foreman edited the commit log and removed the leftover
initialization of 'size']

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
1 file changed