drm/amd/pm: fix the Out-of-bounds read warning

using index i - 1U may beyond element index
for mc_data[] when i = 0.
Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Reviewed-by: Tim Huang <Tim.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/powerplay/hwmgr/ppatomctrl.c

@@ -73,8 +73,9 @@ static int atomctrl_retrieve_ac_timing(
 					j++;
 				} else if ((table->mc_reg_address[i].uc_pre_reg_data &
 							LOW_NIBBLE_MASK) == DATA_EQU_PREV) {
-					table->mc_reg_table_entry[num_ranges].mc_data[i] =
-						table->mc_reg_table_entry[num_ranges].mc_data[i-1];
+					if (i)
+						table->mc_reg_table_entry[num_ranges].mc_data[i] =
+							table->mc_reg_table_entry[num_ranges].mc_data[i-1];
 				}
 			}
 			num_ranges++;