In preparation of changing the type of some parameters
of test_hkdf() from `char *` to `data_t` to get rid of the
calls to mbedtls_test_unhexify():
- Align naming of variables related to the expected okm
- Rename `okm_hex[]` to `okm_string[]`
- Added TEST_ASSERT( expected_okm_len <= sizeof( okm ) ) to check
that the okm[] buffer is large enough for the okm output.
Signed-off-by: Ronald Cron <ronald.cron@arm.com>
4030833bfe