ide: ide-cd_ioctl.c fix sparse integer as NULL pointer warnings

The function ide_cd_queue_pc should be checked as the bufflen arg is
dereferenced and lots of callers are passing in NULL.

drivers/ide/ide-cd_ioctl.c:124:46: warning: Using plain integer as NULL pointer
drivers/ide/ide-cd_ioctl.c:149:47: warning: Using plain integer as NULL pointer
drivers/ide/ide-cd_ioctl.c:231:46: warning: Using plain integer as NULL pointer
drivers/ide/ide-cd_ioctl.c:374:46: warning: Using plain integer as NULL pointer

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>