vt: might_sleep() annotation for do_blank_screen

For symmetry reasons with do_unblank_screen, except without the
oops_in_progress special case.

Just a drive-by annotation while I'm trying to untangle the fbcon vs.
fbdev screen blank/unblank maze.

Signed-off-by: Daniel Vetter <[email protected]>
Reviewed-by: Sam Ravnborg <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Reviewed-by: Maarten Lankhorst <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Nicolas Pitre <[email protected]>
Cc: Adam Borowski <[email protected]>
Cc: Martin Hostettler <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Mikulas Patocka <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: danvet

drivers/tty/vt/vt.c

@@ -4166,6 +4166,8 @@ void do_blank_screen(int entering_gfx)
 	struct vc_data *vc = vc_cons[fg_console].d;
 	int i;
 
+	might_sleep();
+
 	WARN_CONSOLE_UNLOCKED();
 
 	if (console_blanked) {