ide-disk: use ata_id_wcache_enabled()

Replace open-coded check by ata_id_wcache_enabled()
(which also checks validity of word 85).

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/ide-disk.c b/drivers/ide/ide-disk.c
index 8f1ec03..696658d 100644
--- a/drivers/ide/ide-disk.c
+++ b/drivers/ide/ide-disk.c
@@ -889,7 +889,7 @@
 			 drive->bios_cyl, drive->bios_head, drive->bios_sect);
 
 	/* write cache enabled? */
-	if ((id[ATA_ID_CSFO] & 1) || (id[ATA_ID_CFS_ENABLE_1] & (1 << 5)))
+	if ((id[ATA_ID_CSFO] & 1) || ata_id_wcache_enabled(id))
 		drive->wcache = 1;
 
 	write_cache(drive, 1);