[SCSI] scsi_lib: fix recognition of cache type of Initio SBP-2 bridges

Regardless what mode page was asked for, Initio INIC-14x0 and
INIC-2430 always return page 6 without mode page headers.  Try to
recognise this as a special case in scsi_mode_sense and setting the
mode sense headers accordingly.

Signed-off-by: Al Viro <viro@ftp.linux.org.uk>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>