drm/amd/powerplay: return errno code to caller when error occur

return errno code to caller when error occur, and meanwhile
remove gcc '-Wunused-but-set-variable' warning.

drivers/gpu/drm/amd/amdgpu/../powerplay/smumgr/vegam_smumgr.c: In function vegam_populate_smc_boot_level:
drivers/gpu/drm/amd/amdgpu/../powerplay/smumgr/vegam_smumgr.c:1364:6: warning: variable result set but not used [-Wunused-but-set-variable]
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/powerplay/smumgr/vegam_smumgr.c

@@ -1371,11 +1371,16 @@ static int vegam_populate_smc_boot_level(struct pp_hwmgr *hwmgr,
 	result = phm_find_boot_level(&(data->dpm_table.sclk_table),
 			data->vbios_boot_state.sclk_bootup_value,
 			(uint32_t *)&(table->GraphicsBootLevel));
+	if (result)
+		return result;
 
 	result = phm_find_boot_level(&(data->dpm_table.mclk_table),
 			data->vbios_boot_state.mclk_bootup_value,
 			(uint32_t *)&(table->MemoryBootLevel));
 
+	if (result)
+		return result;
+
 	table->BootVddc  = data->vbios_boot_state.vddc_bootup_value *
 			VOLTAGE_SCALE;
 	table->BootVddci = data->vbios_boot_state.vddci_bootup_value *