libata: implement and use ata_noop_irq_clear()

->irq_clear() is used to clear IRQ bit of a SFF controller and isn't
useful for drivers which don't use libata SFF HSM implementation.
However, it's a required callback and many drivers implement their own
noop version as placeholder.  This patch implements ata_noop_irq_clear
and use it to replace those custom placeholders.

Also, SFF drivers which don't support BMDMA don't need to use
ata_bmdma_irq_clear().  It becomes noop if BMDMA address isn't
initialized.  Convert them to use ata_noop_irq_clear().

Signed-off-by: Tejun Heo <htejun@gmail.com>
diff --git a/drivers/ata/pata_icside.c b/drivers/ata/pata_icside.c
index f97068b..e1230ca 100644
--- a/drivers/ata/pata_icside.c
+++ b/drivers/ata/pata_icside.c
@@ -322,11 +322,6 @@
 	.bios_param		= ata_std_bios_param,
 };
 
-/* wish this was exported from libata-core */
-static void ata_dummy_noret(struct ata_port *port)
-{
-}
-
 static void pata_icside_postreset(struct ata_link *link, unsigned int *classes)
 {
 	struct ata_port *ap = link->ap;
@@ -380,7 +375,7 @@
 	.error_handler		= pata_icside_error_handler,
 	.post_internal_cmd	= pata_icside_bmdma_stop,
 
-	.irq_clear		= ata_dummy_noret,
+	.irq_clear		= ata_noop_irq_clear,
 	.irq_on			= ata_irq_on,
 
 	.bmdma_stop		= pata_icside_bmdma_stop,