Tidy up some PSK cipher checks.

The only PSK cipher suite that computes the shared secret early is PSK. Also
there were two (unreachable because of earlier checks) codepaths where we're
exit this function without a master secret.

Change-Id: I3b64fc007b83c4bc46ddb6e14382fb285d8095f9
Reviewed-on: https://boringssl-review.googlesource.com/1172
Reviewed-by: Adam Langley <agl@google.com>
1 file changed