drm/amd/powerplay: fix struct init in renoir_print_clk_levels

drivers/gpu/drm/amd/powerplay/renoir_ppt.c:186:2: error: missing braces
around initializer [-Werror=missing-braces]
  SmuMetrics_t metrics = {0};
    ^

Fixes: 8b803170 ("drm/amd/powerplay: implement sysfs for getting dpm clock")

Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>