ide-atapi: accomodate transfer length calculation for ide-cd

... by factoring it out of ide_cd_do_request() into a helper, as suggested by
Bart.

There should be no functionality change resulting from this patch.

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
[bart: BLK_DEV_IDECD needs to select IDE_ATAPI now]
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/Kconfig b/drivers/ide/Kconfig
index 937945e..4ee85fc 100644
--- a/drivers/ide/Kconfig
+++ b/drivers/ide/Kconfig
@@ -137,6 +137,7 @@
 
 config BLK_DEV_IDECD
 	tristate "Include IDE/ATAPI CDROM support"
+	select IDE_ATAPI
 	---help---
 	  If you have a CD-ROM drive using the ATAPI protocol, say Y. ATAPI is
 	  a newer protocol used by IDE CD-ROM and TAPE drives, similar to the