Vulkan: Fix r_gamma modifications to take immediate effect when r_fbo 1

Modifying r_gamma had no immediate effect with FBO enabled, because the pipelines were not updating.

- broken in this commit: e0d1076

codemp/rd-vulkan/tr_cmds.cpp

@@ -391,6 +391,7 @@ void RE_BeginFrame( stereoFrame_t stereoFrame ) {
 	if ( r_textureMode->modified ) {
 		vk_texture_mode( r_textureMode->string, qfalse );
 		r_textureMode->modified = qfalse;
+		vk_update_post_process_pipelines();
 	}
 
 	//
@@ -402,6 +403,7 @@ void RE_BeginFrame( stereoFrame_t stereoFrame ) {
 		r_dither->modified = qfalse;
 
 		R_SetColorMappings();
+		vk_update_post_process_pipelines();
 	}
 
 	if ( cl_ratioFix->modified ) {