drm/amd/display: fix duplicate assignments

The .set_odm_combine callback pointer was added twice, causing
a harmless -Wextra warning:

drivers/gpu/drm/amd/amdgpu/../display/dc/dcn314/dcn314_optc.c:258:36: error: initialized field overwritten [-Werror=override-init]
  258 |                 .set_odm_combine = optc314_set_odm_combine,
      |                                    ^~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn314/dcn314_optc.c:258:36: note: (near initialization for 'dcn314_tg_funcs.set_odm_combine')

Fixes: 5ade1b95 ("drm/amd/display: Add OTG/ODM functions")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>