PSA buffers and their length should follow a pattern for which
the latter is named after the former as <buffer_name>_length,
but this was not the case for psa_key_derivation_verify_bytes().
This makes life of crypto.h parsers (for automatic code generation)
harder. This commit aims at solving this problem.
Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
