ide: use ->tf_read in ide_read_error()

* Add IDE_TFLAG_IN_FEATURE taskfile flag for reading Feature
  register and handle it in ->tf_read.

* Convert ide_read_error() to use ->tf_read instead of ->INB,
  then uninline and export it.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/pci/ns87415.c b/drivers/ide/pci/ns87415.c
index b20e5f0..b9bb842 100644
--- a/drivers/ide/pci/ns87415.c
+++ b/drivers/ide/pci/ns87415.c
@@ -88,6 +88,8 @@
 	/* be sure we're looking at the low order bits */
 	outb(ATA_DEVCTL_OBS & ~0x80, io_ports->ctl_addr);
 
+	if (task->tf_flags & IDE_TFLAG_IN_FEATURE)
+		tf->feature = inb(io_ports->feature_addr);
 	if (task->tf_flags & IDE_TFLAG_IN_NSECT)
 		tf->nsect  = inb(io_ports->nsect_addr);
 	if (task->tf_flags & IDE_TFLAG_IN_LBAL)