drm/amd/display: fix a compile warning

Fix comile warning like,
  CC [M]  drivers/gpu/drm/i915/gvt/execlist.o
  CC [M]  drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.o
  CC [M]  drivers/gpu/drm/radeon/btc_dpm.o
  CC [M]  drivers/isdn/hisax/avm_a1p.o
  CC [M]  drivers/gpu/drm/amd/amdgpu/../display/dc/dcn10/dcn10_dpp.o
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn10/dcn10_hw_sequencer.c: In function ‘dcn10_update_mpcc’:
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn10/dcn10_hw_sequencer.c:1903:9: warning: missing braces around initializer [-Wmissing-braces]
  struct mpcc_blnd_cfg blnd_cfg = {0};
         ^
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn10/dcn10_hw_sequencer.c:1903:9: warning: (near initialization for ‘blnd_cfg.black_color’) [-Wmissing-braces]

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>