riscv: cpu: Skip unavailable hart in the get_count() op

We should not count in hart that is marked as not available in the
device tree in riscv_cpu_get_count().

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
diff --git a/drivers/cpu/riscv_cpu.c b/drivers/cpu/riscv_cpu.c
index f77c126..28ad0aa 100644
--- a/drivers/cpu/riscv_cpu.c
+++ b/drivers/cpu/riscv_cpu.c
@@ -46,6 +46,10 @@
 	ofnode_for_each_subnode(node, dev_ofnode(dev->parent)) {
 		const char *device_type;
 
+		/* skip if hart is marked as not available in the device tree */
+		if (!ofnode_is_available(node))
+			continue;
+
 		device_type = ofnode_read_string(node, "device_type");
 		if (!device_type)
 			continue;