drm/amd/display: cleanup extern usage in function definition

Smatch reports this issue
hdcp1_execution.c:500:29: warning: function
  'mod_hdcp_hdcp1_dp_execution' with external linkage
  has definition

The storage-class-specifier extern is not needed in a
definition, so remove it.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c

@@ -497,9 +497,9 @@ enum mod_hdcp_status mod_hdcp_hdcp1_execution(struct mod_hdcp *hdcp,
 	return status;
 }
 
-extern enum mod_hdcp_status mod_hdcp_hdcp1_dp_execution(struct mod_hdcp *hdcp,
-		struct mod_hdcp_event_context *event_ctx,
-		struct mod_hdcp_transition_input_hdcp1 *input)
+enum mod_hdcp_status mod_hdcp_hdcp1_dp_execution(struct mod_hdcp *hdcp,
+						 struct mod_hdcp_event_context *event_ctx,
+						 struct mod_hdcp_transition_input_hdcp1 *input)
 {
 	enum mod_hdcp_status status = MOD_HDCP_STATUS_SUCCESS;