libteeacl: use realloc() instead of reallocarray()

Use realloc() instead of reallocarray(), since uClibc apparently does
not implement reallocarray().

Fixes: https://github.com/OP-TEE/optee_client/issues/339



Signed-off-by: Eero Aaltonen <eero.aaltonen@vaisala.com>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>