drm/qxl: don't allocate a dma_address array

That seems to be unused.

Daniel: Mike reported a warning when booting with qxl, which this
patch fixes:

[    1.815561] WARNING: CPU: 7 PID: 355 at drivers/gpu/drm/ttm/ttm_pool.c:365 ttm_pool_alloc+0x41b/0x540 [ttm]

Signed-off-by: Christian König <christian.koenig@amd.com>
Reported-by: Mike Galbraith <efault@gmx.de>
Tested-by: Mike Galbraith <efault@gmx.de>
References: https://lore.kernel.org/lkml/7cb43d5b-4e6a-defc-1ab6-5f713ad5a963@amd.com/


Reviewed-by: David Airlie <airlied@redhat.com>
[davnet: bring commit message up to par.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201218134243.110884-1-christian.koenig@amd.com