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]