Fixing SetAttestationKey command flow

Fixing bug based on the assumption that data received on
SetAttestationKey was already a protobuf.
New flow follows what is done on C++ KeyMint.

Bug: 258602662
Test: Build.py, run keymint TA unittests
Change-Id: I0c27b6947f0447666dd8d70409998026f7f6a1bb
1 file changed