drm/amd/display: remove set but not used variable 'mc_vm_apt_default'

drivers/gpu/drm/amd/amdgpu/../display/dc/dcn21/dcn21_hubp.c:
 In function hubp21_set_vm_system_aperture_settings:
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn21/dcn21_hubp.c:343:23:
 warning: variable mc_vm_apt_default set but not used [-Wunused-but-set-variable]

It is never used, so remove it.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn21/dcn21_hubp.c

@@ -340,13 +340,9 @@ void hubp21_set_vm_system_aperture_settings(struct hubp *hubp,
 {
 	struct dcn21_hubp *hubp21 = TO_DCN21_HUBP(hubp);
 
-	PHYSICAL_ADDRESS_LOC mc_vm_apt_default;
 	PHYSICAL_ADDRESS_LOC mc_vm_apt_low;
 	PHYSICAL_ADDRESS_LOC mc_vm_apt_high;
 
-	// The format of default addr is 48:12 of the 48 bit addr
-	mc_vm_apt_default.quad_part = apt->sys_default.quad_part >> 12;
-
 	// The format of high/low are 48:18 of the 48 bit addr
 	mc_vm_apt_low.quad_part = apt->sys_low.quad_part >> 18;
 	mc_vm_apt_high.quad_part = apt->sys_high.quad_part >> 18;