cmd64x: set IDE_HFLAG_SERIALIZE explictly for CMD646

* Set IDE_HFLAG_SERIALIZE explictly for CMD646.

* Remove no longer needed ide_cmd646 chipset type (which has
  a nice side-effect of fixing handling of unexpected IRQs).

Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/ide-probe.c b/drivers/ide/ide-probe.c
index b0f9ede..a0eb72e 100644
--- a/drivers/ide/ide-probe.c
+++ b/drivers/ide/ide-probe.c
@@ -1125,7 +1125,7 @@
 		sa = IRQF_SHARED;
 #endif /* __mc68000__ */
 
-		if (hwif->chipset == ide_pci || hwif->chipset == ide_cmd646)
+		if (hwif->chipset == ide_pci)
 			sa = IRQF_SHARED;
 
 		if (io_ports->ctl_addr)