configure-instance.in: fix typo

$caddr is not defined so this test was in fact [ -f "/$file" ]. Most likely the root directory does not contain hashed cert files or ca-certificates.crt, which means that all files were deleted from the CApath directory in the chroot. However, the files are copied back into the chroot by the next command, so this shouldn't have caused any issues aside from a bit of extra work.