MSI/powerpc: Use __read_msi_msg() instead of read_msi_msg()

rtas_setup_msi_irqs() already has the struct msi_desc pointer required by
__read_msi_msg(), so call it directly instead of having read_msi_msg() look
it up from the IRQ.

No functional change.

[bhelgaas: changelog]
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: linuxppc-dev@lists.ozlabs.org

arch/powerpc/platforms/pseries/msi.c

@@ -476,7 +476,7 @@ again:
 		irq_set_msi_desc(virq, entry);
 
 		/* Read config space back so we can restore after reset */
-		read_msi_msg(virq, &msg);
+		__read_msi_msg(entry, &msg);
 		entry->msg = msg;
 	}