drm/amd/display: Fix memory leak in dm_set_writeback()

'wb_info' needs to be freed on error paths or it would leak the memory.

Smatch pointed this out.

Fixes: c81e13b9 ("drm/amd/display: Hande writeback request from userspace")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -8879,12 +8879,14 @@ static void dm_set_writeback(struct amdgpu_display_manager *dm,
 	acrtc = to_amdgpu_crtc(wb_conn->encoder.crtc);
 	if (!acrtc) {
 		DRM_ERROR("no amdgpu_crtc found\n");
+		kfree(wb_info);
 		return;
 	}
 
 	afb = to_amdgpu_framebuffer(new_con_state->writeback_job->fb);
 	if (!afb) {
 		DRM_ERROR("No amdgpu_framebuffer found\n");
+		kfree(wb_info);
 		return;
 	}