ipr: qc_fill_rtf() method should not store alternate status register

The 'ctl' field of  the 'struct ata_taskfile' is not really dual purpose, i.e.
it is not intended  for storing the alternate status register (which is mapped
at the same address in the legacy IDE controllers) in the qc_fill_rtf() method.
No other 'libata' driver except 'drivers/scsi/ipr.c' stores the alternate status
register's value in the 'ctl' field of 'qc->result_tf', hence this driver should
not do this as well...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>