drm/radeon: remove redundant assignment to reg

The pointer reg is being assigned a value that is not read, the
exit path via label 'out' never accesses it. The assignment is
redundant and can be removed.

Cleans up clang scan build warning:
drivers/gpu/drm/radeon/radeon_object.c:570:3: warning: Value
stored to 'reg' is never read [deadcode.DeadStores]
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_object.c

@@ -567,7 +567,6 @@ int radeon_bo_get_surface_reg(struct radeon_bo *bo)
 		return 0;
 
 	if (bo->surface_reg >= 0) {
-		reg = &rdev->surface_regs[bo->surface_reg];
 		i = bo->surface_reg;
 		goto out;
 	}