Revert "ptp: Fixes a null pointer dereference in ptp_ioctl"

This reverts commit 8a4f030d.

Richard says:

  The test itself is harmless, but keeping it will make people think,
  "oh this pointer can be invalid."

  In fact the core stack ensures that ioctl() can't be invoked after
  release(), otherwise Bad Stuff happens.

Fixes: 8a4f030d

 ("ptp: Fixes a null pointer dereference in ptp_ioctl")
Link: https://lore.kernel.org/all/ZVAf_qdRfDAQYUt-@hoboy.vegasvil.org/
Signed-off-by: Jakub Kicinski <kuba@kernel.org>