[bootlin/training-materials] 1b386a: Makefile: correct fix for double slash issue

[Thomas Petazzoni]

  Branch: refs/heads/master
  Home:   https://github.com/bootlin/training-materials
  Commit: 1b386a5697bd1569fd31a1c3c1984e9a34a1133f
      https://github.com/bootlin/training-materials/commit/1b386a5697bd1569fd31a1c3c1984e9a34a1133f
  Author: Thomas Petazzoni <thomas.petazzoni at bootlin.com>
  Date:   2022-10-05 (Wed, 05 Oct 2022)

  Changed paths:
    M Makefile
    M labs/setup/setup.tex

  Log Message:
  -----------
  Makefile: correct fix for double slash issue

Also need to re-add the slash in the setup lab.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni at bootlin.com>