[bootlin/training-materials] de11c4: Embedeed Linux: fix ubifsmount command

[Michael Opdenacker]

  Branch: refs/heads/master
  Home:   https://github.com/bootlin/training-materials
  Commit: de11c4074ad0f3cffe158a6c1225360245030e0b
      https://github.com/bootlin/training-materials/commit/de11c4074ad0f3cffe158a6c1225360245030e0b
  Author: Michael Opdenacker <michael.opdenacker at bootlin.com>
  Date:   2022-04-11 (Mon, 11 Apr 2022)

  Changed paths:
    M slides/sysdev-flash-filesystems/sysdev-flash-filesystems.tex

  Log Message:
  -----------
  Embedeed Linux: fix ubifsmount command

Not very consistent with the other commands, but
even after running "ubi part UBI",

"ubifsmount rootfs" doesn't work
but "ubifs ubi0:rootfs" does work.

Signed-off-by: Michael Opdenacker <michael.opdenacker at bootlin.com>