KEYS: trusted: Fix memory leak on object td

Two error return paths are neglecting to free allocated object td,
causing a memory leak. Fix this by returning via the error return
path that securely kfree's td.

Fixes clang scan-build warning:
security/keys/trusted-keys/trusted_tpm1.c:496:10: warning: Potential
memory leak [unix.Malloc]

Cc: stable@vger.kernel.org
Fixes: 5df16caa

 ("KEYS: trusted: Fix incorrect handling of tpm_get_random()")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>