[BRLTTY] Create special devices within a private area.

[Samuel Thibault]

Hello,

commit f16d75072983 ("Create special devices within a private area.")
broke the integration of brltty in initramfs: at boot we get 

mount: mounting /dev on /root/dev failed: Invalid argument
mount: mounting /dev on /root/dev failed: Invalid argument
mount: mounting /run on /root/run failed: Invalid argument
mount: mounting /sys on /root/sys failed: Invalid argument
mount: mounting /proc on /root/proc failed: Invalid argument
run-init: error moving root: Invalid argument

and booting stops there, making the system unbootable. I tried 6.9 +
reverting this, and the boot works again.

Was this tested with initramfs integration, perhaps something is needed
in that case?  I am here using initramfs-tools (0.148.3 or 0.150 with
same effect)

Samuel