drm/vmwgfx: Remove set but not used variable 'file_priv'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/vmwgfx/vmwgfx_fence.c: In function 'vmw_event_fence_action_seq_passed':
drivers/gpu/drm/vmwgfx/vmwgfx_fence.c:909:19: warning:
 variable 'file_priv' set but not used [-Wunused-but-set-variable]
  struct drm_file *file_priv;

It not used any more since
commit fb740cf2 ("drm: Create drm_send_event helpers")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>