ata_tf_read was setting HOB bit when lba48 command was submitted, but
was not clearing it before reading "normal" data.  As it is only place
which sets HOB bit in control register, and register reads should not
be affected by other bits, let's just clear it when we are done with
reading upper bytes so non-48bit commands do not have to touch ctl
at all.

pata_scc suffered from same problem...
Signed-off-by: Petr Vandrovec <petr@vandrovec.name>
Signed-off-by: Jeff Garzik <jeff@garzik.org>