drm/amd/display: Drop unnecessary ret variable for enable_assr()

[Why]
enable_assr() has a res variable that only is changed in one block with
no cleanup necessary.

[How]
Remove variable and return early from failure cases.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_hdcp.c

@@ -457,7 +457,6 @@ static bool enable_assr(void *handle, struct dc_link *link)
 	struct mod_hdcp hdcp = hdcp_work->hdcp;
 	struct psp_context *psp = hdcp.config.psp.handle;
 	struct ta_dtm_shared_memory *dtm_cmd;
-	bool res = true;
 
 	if (!psp->dtm_context.context.initialized) {
 		DRM_INFO("Failed to enable ASSR, DTM TA is not initialized.");
@@ -478,10 +477,10 @@ static bool enable_assr(void *handle, struct dc_link *link)
 
 	if (dtm_cmd->dtm_status != TA_DTM_STATUS__SUCCESS) {
 		DRM_INFO("Failed to enable ASSR");
-		res = false;
+		return false;
 	}
 
-	return res;
+	return true;
 }
 
 static void update_config(void *handle, struct cp_psp_stream_config *config)