tx4939ide: Do not use zero count PRD entry

This fixes data corruption on some heavy load.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: stable <stable@kernel.org>
Cc: sshtylyov@ru.mvista.com
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/tx4939ide.c

@@ -259,6 +259,12 @@ static int tx4939ide_build_dmatable(ide_drive_t *drive, struct request *rq)
 			bcount = 0x10000 - (cur_addr & 0xffff);
 			if (bcount > cur_len)
 				bcount = cur_len;
+			/*
+			 * This workaround for zero count seems required.
+			 * (standard ide_build_dmatable do it too)
+			 */
+			if ((bcount & 0xffff) == 0x0000)
+				bcount = 0x8000;
 			*table++ = bcount & 0xffff;
 			*table++ = cur_addr;
 			cur_addr += bcount;