drm/radeon: fix possible segfault when parsing pm tables

If we have a empty power table, bail early and allocate
the default power state.

Should fix:
https://bugs.freedesktop.org/show_bug.cgi?id=63865

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/radeon_atombios.c

@@ -2028,6 +2028,8 @@ static int radeon_atombios_parse_power_table_1_3(struct radeon_device *rdev)
 	num_modes = power_info->info.ucNumOfPowerModeEntries;
 	if (num_modes > ATOM_MAX_NUMBEROF_POWER_BLOCK)
 		num_modes = ATOM_MAX_NUMBEROF_POWER_BLOCK;
+	if (num_modes == 0)
+		return state_index;
 	rdev->pm.power_state = kzalloc(sizeof(struct radeon_power_state) * num_modes, GFP_KERNEL);
 	if (!rdev->pm.power_state)
 		return state_index;
@@ -2432,6 +2434,8 @@ static int radeon_atombios_parse_power_table_4_5(struct radeon_device *rdev)
 	power_info = (union power_info *)(mode_info->atom_context->bios + data_offset);
 
 	radeon_atombios_add_pplib_thermal_controller(rdev, &power_info->pplib.sThermalController);
+	if (power_info->pplib.ucNumStates == 0)
+		return state_index;
 	rdev->pm.power_state = kzalloc(sizeof(struct radeon_power_state) *
 				       power_info->pplib.ucNumStates, GFP_KERNEL);
 	if (!rdev->pm.power_state)
@@ -2530,6 +2534,8 @@ static int radeon_atombios_parse_power_table_6(struct radeon_device *rdev)
 	non_clock_info_array = (struct _NonClockInfoArray *)
 		(mode_info->atom_context->bios + data_offset +
 		 le16_to_cpu(power_info->pplib.usNonClockInfoArrayOffset));
+	if (state_array->ucNumEntries == 0)
+		return state_index;
 	rdev->pm.power_state = kzalloc(sizeof(struct radeon_power_state) *
 				       state_array->ucNumEntries, GFP_KERNEL);
 	if (!rdev->pm.power_state)
@@ -2620,7 +2626,9 @@ void radeon_atombios_get_power_modes(struct radeon_device *rdev)
 		default:
 			break;
 		}
-	} else {
+	}
+
+	if (state_index == 0) {
 		rdev->pm.power_state = kzalloc(sizeof(struct radeon_power_state), GFP_KERNEL);
 		if (rdev->pm.power_state) {
 			rdev->pm.power_state[0].clock_info =