drm/vkms: Fix flush_work() without INIT_WORK().

syzbot is hitting a lockdep warning [1] because flush_work() is called
without INIT_WORK() after kzalloc() at vkms_atomic_crtc_reset().

Commit 6c234fe3 ("drm/vkms: Implement CRC debugfs API") added
INIT_WORK() to only vkms_atomic_crtc_duplicate_state() side. Assuming
that lifecycle of crc_work is appropriately managed, fix this problem
by adding INIT_WORK() to vkms_atomic_crtc_reset() side.

[1] https://syzkaller.appspot.com/bug?id=a5954455fcfa51c29ca2ab55b203076337e1c770



Reported-and-tested-by: syzbot <syzbot+12f1b031b6da017e34f8@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Shayenne Moura <shayenneluzmoura@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1547829823-9877-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp