qnx4: convert qnx4 to use the new mount api

Convert the qnx4 filesystem to use the new mount API.

Tested mount, umount, and remount using a qnx4 boot image.

Signed-off-by: Bill O'Donnell <bodonnel@redhat.com>
Link: https://lore.kernel.org/r/20240229161649.800957-1-bodonnel@redhat.com


Acked-by: Anders Larsen <al@alarsen.net>
Signed-off-by: Christian Brauner <brauner@kernel.org>