kms: fix build
Fix the following build error:
../../modules/video_output/kms.c: In function ‘WindowEnable’:
../../modules/video_output/kms.c:335:9: error: a label can only be part of a statement and a declaration is not a statement
335 | struct drm_mode_destroy_dumb destroy_request = {
With gcc version 10.2.1 20210110 (Debian 10.2.1-6) and -fsanitize=thread