drm/amd/display: Check index msg_id before read or write

[WHAT]
msg_id is used as an array index and it cannot be a negative value, and
therefore cannot be equal to MOD_HDCP_MESSAGE_ID_INVALID (-1).

[HOW]
Check whether msg_id is valid before reading and setting.

This fixes 4 OVERRUN issues reported by Coverity.

Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Alex Hung

drivers/gpu/drm/amd/display/modules/hdcp/hdcp_ddc.c

@@ -156,6 +156,10 @@ static enum mod_hdcp_status read(struct mod_hdcp *hdcp,
 	uint32_t cur_size = 0;
 	uint32_t data_offset = 0;
 
+	if (msg_id == MOD_HDCP_MESSAGE_ID_INVALID) {
+		return MOD_HDCP_STATUS_DDC_FAILURE;
+	}
+
 	if (is_dp_hdcp(hdcp)) {
 		while (buf_len > 0) {
 			cur_size = MIN(buf_len, HDCP_MAX_AUX_TRANSACTION_SIZE);
@@ -215,6 +219,10 @@ static enum mod_hdcp_status write(struct mod_hdcp *hdcp,
 	uint32_t cur_size = 0;
 	uint32_t data_offset = 0;
 
+	if (msg_id == MOD_HDCP_MESSAGE_ID_INVALID) {
+		return MOD_HDCP_STATUS_DDC_FAILURE;
+	}
+
 	if (is_dp_hdcp(hdcp)) {
 		while (buf_len > 0) {
 			cur_size = MIN(buf_len, HDCP_MAX_AUX_TRANSACTION_SIZE);