disable parallel build for syncd and syncd-rpc (sonic-net#225)

Author: lguohan

debian/rules

@@ -30,7 +30,7 @@ binary-syncd:
 	dh build  -N syncd-rpc -N syncd-rpc-dbg --with autotools-dev
 	dh binary -N syncd-rpc -N syncd-rpc-dbg --with autotools-dev
 
-binary-syncd-rpc:
+binary-syncd-rpc: | binary-syncd
 	$(shell echo '--enable-rpcserver=no' > /tmp/syncd-build)
 	dh clean  --with autotools-dev
 	dh build  -N syncd -N syncd-dbg --with autotools-dev