[PATCH] sil24: implement tf_read callback

 Hello, guys.

 This patch implements ->tf_read callback for sil24.  It didn't use to
be necessary but new ata_gen_fixed_sense now makes use of ->tf_read
callback.  This patch is taken from Edward Falk's driver.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>