drm/tegra: Make gather_bo_ops static

The symbol is not used outside of the file, so mark it static.

Fixes the following warning:

./drivers/gpu/drm/tegra/submit.c:136:28: warning: symbol 'gather_bo_ops'
was not declared. Should it be static?
Signed-off-by: Nruanjinjie <ruanjinjie@huawei.com>
Signed-off-by: NThierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/submit.c

@@ -133,7 +133,7 @@ static void gather_bo_munmap(struct host1x_bo *host_bo, void *addr)
 {
 }
 
-const struct host1x_bo_ops gather_bo_ops = {
+static const struct host1x_bo_ops gather_bo_ops = {
 	.get = gather_bo_get,
 	.put = gather_bo_put,
 	.pin = gather_bo_pin,