commsec encrypt: get rid of unnecessary intermediate value
commsec encrypt: get rid of unnecessary intermediate value

* was reviewing the generated C and it looked funny. There's
  no need to copy the argument mavStream to the stack only to
  copy it into the pkg array right afterwards.
* maybe at one point copyToPkg had a less general type signature
  or something

GaloisInc/ivory-tower-stm32,GaloisInc/ivory-tower-stm32,GaloisInc/ivory-tower-stm32