drm/qxl: use flexible-array member instead of zero-length array

drm/qxl: use flexible-array member instead of zero-length array

Use flexible-array member introduced in C99 instead of zero-length
array. Most of zero-length array was already taken care in previous
patch [1]. Now modified few more cases which were not handled earlier.

[1]. https://patchwork.kernel.org/patch/11394197/

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1607650349-28513-1-git-send-email-tiantao6@hisilicon.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>