core.ControlWord: fix missing s

src/main/scala/uk/ac/soton/ecs/can/core/ControlWord.scala

@@ -11,7 +11,7 @@ class ControlWord(addrWidth: Int, immWidth: Int = 8) extends Bundle {
   val relativeBranch = Bool()
   val ramReadAddress = Vec(2, UInt(addrWidth.W))
   val ramWriteAddress = UInt(addrWidth.W)
-  val fillConstant = Bool()
+  val fillConstants = Bool()
   val incrementBlockCount = Bool()
   val roundLoop = Bool()
   val addFrom = Bool()