Decryption calls though multiple threads may result in race conditions
between the setting of the key and the actual call to decryption.
This results in OEMCrypto errors when the buffer type used in
decryption did not match the key selected. This is addressed by
having the the two calls be in the same critical section.
b/11009857
Change-Id: I74f1a0689ca17114f3cdd029022013b05c415acd
a74980b2f1