drm/amd/display: Make calculate_integer_scaling static

Fix sparse warning:

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_resource.c:963:6:
 warning: symbol 'calculate_integer_scaling' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_resource.c

@@ -960,7 +960,7 @@ static bool are_rects_integer_multiples(struct rect src, struct rect dest)
 	return false;
 }
 
-void calculate_integer_scaling(struct pipe_ctx *pipe_ctx)
+static void calculate_integer_scaling(struct pipe_ctx *pipe_ctx)
 {
 	if (!pipe_ctx->plane_state->scaling_quality.integer_scaling)
 		return;