mailbox: zynqmp: Fix counts of child nodes

If child mailbox node status is disabled it causes
crash in interrupt handler. Fix this by assigning
only available child node during driver probe.

Fixes: 4981b82ba2ff ("mailbox: ZynqMP IPI mailbox controller")
Signed-off-by: Tanmay Shah <[e-mail]>
Acked-by: Michal Simek <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mathieu Poirier <[e-mail]>

drivers/mailbox/zynqmp-ipi-mailbox.c

···
 	struct zynqmp_ipi_mbox *mbox;
 	int num_mboxes, ret = -EINVAL;
 
-	num_mboxes = of_get_child_count(np);
+	num_mboxes = of_get_available_child_count(np);
+	if (num_mboxes == 0) {
+		dev_err(dev, "mailbox nodes not available\n");
+		return -EINVAL;
+	}
+
 	pdata = devm_kzalloc(dev, struct_size(pdata, ipi_mboxes, num_mboxes),
 			     GFP_KERNEL);
 	if (!pdata)