Fix the following gcc warning:

drivers/video/fbdev/aty/aty128fb.c:337:36: warning: ‘sdr_64’ defined but
not used [-Wunused-const-variable=]
 static const struct aty128_meminfo sdr_64 = {
                                    ^~~~~~
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200417092318.13978-1-yanaijie@huawei.com