libata: don't check whether to use DMA or not for no data commands

There's no reason to check whether to use DMA or not for no data
commands.  Don't do it.  While at it, make local variable using_pio in
atapi_xlat() set iff ATAPI_PROT_PIO is going to be used and rename
ata_check_atapi_dma() to atapi_check_dma() for consistency.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index cc816ca..303fc0d 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4297,7 +4297,7 @@
 }
 
 /**
- *	ata_check_atapi_dma - Check whether ATAPI DMA can be supported
+ *	atapi_check_dma - Check whether ATAPI DMA can be supported
  *	@qc: Metadata associated with taskfile to check
  *
  *	Allow low-level driver to filter ATA PACKET commands, returning
@@ -4310,7 +4310,7 @@
  *	RETURNS: 0 when ATAPI DMA can be used
  *               nonzero otherwise
  */
-int ata_check_atapi_dma(struct ata_queued_cmd *qc)
+int atapi_check_dma(struct ata_queued_cmd *qc)
 {
 	struct ata_port *ap = qc->ap;