fbcon: set_con2fb_map needs to set con2fb_map!

I got really badly confused in d443d93864 ("fbcon: move more common
code into fb_open()") because we set the con2fb_map before the failure
points, which didn't look good.

But in trying to fix that I moved the assignment into the wrong path -
we need to do it for _all_ vc we take over, not just the first one
(which additionally requires the call to con2fb_acquire_newinfo).

I've figured this out because of a KASAN bug report, where the
fbcon_registered_fb and fbcon_display arrays went out of sync in
fbcon_mode_deleted() because the con2fb_map pointed at the old
fb_info, but the modes and everything was updated for the new one.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Helge Deller <deller@gmx.de>
Tested-by: Xingyuan Mo <hdthky0@gmail.com>
Fixes: d443d93864 ("fbcon: move more common code into fb_open()")
Reported-by: Xingyuan Mo <hdthky0@gmail.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Xingyuan Mo <hdthky0@gmail.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Helge Deller <deller@gmx.de>
Cc: <stable@vger.kernel.org> # v5.19+

drivers/video/fbdev/core/fbcon.c

@@ -846,10 +846,11 @@ static int set_con2fb_map(int unit, int newidx, int user)
 		if (err)
 			return err;
 
-		con2fb_map[unit] = newidx;
 		fbcon_add_cursor_work(info);
 	}
 
+	con2fb_map[unit] = newidx;
+
 	/*
 	 * If old fb is not mapped to any of the consoles,
 	 * fbcon should release it.