cryptsetup: avoid a segfault when a keyfile is passed along with a TPM device (#41892)

A segfault is observed when both key_file and tpm2-device are
simultaneously passed to systemd-cryptsetup, e.g.:
  systemd-cryptsetup attach test_data /vol /my-pass tpm2-device=auto

The crash appears after commit 5c6aad9 but the flaw in the logic was
pre-existing.

Fixes #41867

diff --cc test/units/TEST-70-TPM2.cryptsetup.sh
Simple merge