drm/amdgpu: remove 4 set but not used variable in amdgpu_atombios_get_connector_info_from_object_table

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c: In function
'amdgpu_atombios_get_connector_info_from_object_table':
drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c:376:26: warning: variable
'grph_obj_num' set but not used [-Wunused-but-set-variable]
drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c:376:13: warning: variable
'grph_obj_id' set but not used [-Wunused-but-set-variable]
drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c:341:37: warning: variable
'con_obj_type' set but not used [-Wunused-but-set-variable]
drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c:341:24: warning: variable
'con_obj_num' set but not used [-Wunused-but-set-variable]

They are never used, so can be removed.

Fixes: d38ceaf9 ("drm/amdgpu: add core driver (v4)")
Signed-off-by: yu kuai <yukuai3@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>