swtpm_setup: Fix errno comparison on end-of-directory (FreeBSD)

swtpm_setup: Fix errno comparison on end-of-directory (FreeBSD)

FreeBSD may return errno EINVAL beside ENOENT once there are no more
entries in a directory to walk over. It claims that readdir() follows
the getdirentries() return codes, which do include EINVAL but not
ENOENT. But ENOENT is also being used.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>