sata_mv: revert SoC irq breakage

Revert most of commit 6be96ac1d5e4d913e1f48299db083ada5321803b2,
originally from Lennert Buijtenheck (Marvell) and Saeed Bishara (Marvell),
since that commit causes sata_mv to oops at startup on SOC "Kirkwood".

The SOC variants do not have the hpriv->irq_{cause,mask}_ofs registers,
so don't try to write to them!

This patch should also be considered for -stable.
Reported-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/sata_mv.c

@@ -3734,11 +3734,13 @@ static int mv_init_host(struct ata_host *host, unsigned int board_idx)
 		writelfl(0, hc_mmio + HC_IRQ_CAUSE_OFS);
 	}
 
-	/* Clear any currently outstanding host interrupt conditions */
-	writelfl(0, mmio + hpriv->irq_cause_ofs);
+	if (!IS_SOC(hpriv)) {
+		/* Clear any currently outstanding host interrupt conditions */
+		writelfl(0, mmio + hpriv->irq_cause_ofs);
 
-	/* and unmask interrupt generation for host regs */
-	writelfl(hpriv->unmask_all_irqs, mmio + hpriv->irq_mask_ofs);
+		/* and unmask interrupt generation for host regs */
+		writelfl(hpriv->unmask_all_irqs, mmio + hpriv->irq_mask_ofs);
+	}
 
 	/*
 	 * enable only global host interrupts for now.