[PATCH] libata: don't read TF directly from sense generation functions

TF register might not be directly accessible depending on errors.
e.g. TF of failed NCQ command is in log page 10h.  Make reading TF
responsibility of error handlers.  For the current EH, simply push TF
reading into qc completion functions as they are practically part of
EH.  New EH will fill qc->tf with status registers before complting
qcs.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>