minor dzx0_turbo optimization

[ZERICO2005]

I have found a small optimization to dzx0_turbo. Changing ld a, $80 to inc c \ scf allows us to skip a few instructions. I believe this optimization can also be done to dzx0_fast.

dzx0_turbo:
	ld	bc, $ffff		; preserve default offset 1
	ld	(dzx0t_last_offset+1), bc
	inc	bc
-	ld	a, $80
-	jr	dzx0t_literals
+	inc	c
+	scf
	jr	dzx0t_start
	; ...

dzx0t_literals:
	inc	c			; obtain length
	add	a, a
	jp	nz, dzx0t_literals_skip
+ dzx0t_start:
	ld	a, (hl)			; load another group of 8 bits
	inc	hl
	rla
dzx0t_literals_skip: