crypto: ccp - Avoid discarding errors in psp_send_platform_access_msg()

Errors can potentially occur in the "processing" of PSP commands or
commands can be processed successfully but still return an error code in
the header.

This second case was being discarded because PSP communication worked but
the command returned an error code in the payload header.

Capture both cases and return them to the caller as -EIO for the caller
to investigate. The caller can detect the latter by looking at
`req->header->status`.

Reported-and-tested-by: Tim Van Patten <timvp@google.com>
Fixes: 7ccc4f4e ("crypto: ccp - Add support for an interface for platform features")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>