tee-supplicant: Enforce paths bound limits

Verify "ta-path" command line argument length and if snprintf()
concated path is too long, then print an error message and
terminate startup.

Signed-off-by: Tanel Dettenborn <tanel@ssrc.tii.ae>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Acked-by: Etienne Carriere <etienne.carriere@foss.st.com>