ide: move data register access out of tf_{read|load}() methods (take 2)

Move IDE_FTFLAG_{IN|OUT}_DATA flag handling out of tf_{read|load}() methods
into the only two functions where these flags actually need to be handled:
do_rw_taskfile() and ide_complete_cmd()...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>