ide-cd: merge cdrom_write_check_ireason() and cdrom_read_check_ireason()

Add 'rw' parameter to cdrom_read_check_ireason(), make it handle
both read and write checking, rename it to ide_cd_check_ireason(),
finally remove no longer needed cdrom_write_check_ireason().

There should be no functionality changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>