[libata] pata_serverworks: fill in ->irq_clear hook

Required by libata, as it is called unconditionally.

Fixes an obvious oops.

Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/ata/pata_serverworks.c b/drivers/ata/pata_serverworks.c
index 75cc5a2..d62051b 100644
--- a/drivers/ata/pata_serverworks.c
+++ b/drivers/ata/pata_serverworks.c
@@ -356,6 +356,8 @@
 	.data_xfer	= ata_pio_data_xfer,
 
 	.irq_handler	= ata_interrupt,
+	.irq_clear	= ata_bmdma_irq_clear,
+
 	.port_start	= ata_port_start,
 	.port_stop	= ata_port_stop,
 	.host_stop	= ata_host_stop
@@ -389,6 +391,8 @@
 	.data_xfer	= ata_pio_data_xfer,
 
 	.irq_handler	= ata_interrupt,
+	.irq_clear	= ata_bmdma_irq_clear,
+
 	.port_start	= ata_port_start,
 	.port_stop	= ata_port_stop,
 	.host_stop	= ata_host_stop