qemu_tpm: Only warn about missing locking feature on shared filesystems

qemu_tpm: Only warn about missing locking feature on shared filesystems

The warning pollutes the logs and might give a bad impression on someone
reading them even though the locking is not always needed.  This way we
at least limit the logging in unnecessary cases.

Resolves: https://issues.redhat.com/browse/RHEL-80155
Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>