drm/radeon: remove three set but not used variable

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

drivers/gpu/drm/radeon/radeon_atombios.c: In function
‘radeon_get_atom_connector_info_from_object_table’:
drivers/gpu/drm/radeon/radeon_atombios.c:651:26: warning: variable
‘grph_obj_num’ set but not used [-Wunused-but-set-variable]
drivers/gpu/drm/radeon/radeon_atombios.c:651:13: warning: variable
‘grph_obj_id’ set but not used [-Wunused-but-set-variable]
drivers/gpu/drm/radeon/radeon_atombios.c:573:37: warning: variable
‘con_obj_type’ set but not used [-Wunused-but-set-variable]

They are never used, and so can be removed.

Signed-off-by: yu kuai <yukuai3@huawei.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>