make chrin infinte loop until properly implemented

c64/kernal/chrin.s

@@ -4,6 +4,10 @@
 	;; If from keyboard, then it gets a whole line of input, and returns the first char.
 	;; Repeated calls after that read out the successive bytes of the line of input.
 chrin:
+	;; XXX - Not yet implemented, so infinite loop for now
+	inc $d020
+	jmp chrin
+	
 	lda #$00
 	clc
 	rts