amd: display: modules: Remove repeated struct declaration

struct mod_hdcp is declared twice. One is declared at 33rd line.
The blew one is not needed. Remove the duplicate.
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/modules/inc/mod_hdcp.h

@@ -261,8 +261,6 @@ struct mod_hdcp_config {
 	uint8_t index;
 };
 
-struct mod_hdcp;
-
 /* dm allocates memory of mod_hdcp per dc_link on dm init based on memory size*/
 size_t mod_hdcp_get_memory_size(void);