enctreebin: use a local var for encoder sink pad
enctreebin: use a local var for encoder sink pad

Change-Id: I153f2841c5eeefad9ed3217f8bf4fd8f6518c70e

Kurento/kms-core,ESTOS/kms-core,Kurento/kms-core,Kurento/kms-core,ESTOS/kms-core,Kurento/kms-core,ESTOS/kms-core,ESTOS/kms-core