imx: power-domain: Enable refcounting on imx8mp

Prevent enabling/disabling multiple times the same power domain to avoid
breakages due to the same power domains being referenced several times
by different device nodes.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
diff --git a/drivers/power/domain/imx8mp-hsiomix.c b/drivers/power/domain/imx8mp-hsiomix.c
index 455ad53..1ca4388 100644
--- a/drivers/power/domain/imx8mp-hsiomix.c
+++ b/drivers/power/domain/imx8mp-hsiomix.c
@@ -201,8 +201,12 @@
 static int imx8mp_hsiomix_probe(struct udevice *dev)
 {
 	struct imx8mp_hsiomix_priv *priv = dev_get_priv(dev);
+	struct power_domain_plat *plat = dev_get_uclass_plat(dev);
 	int ret;
 
+	/* Definitions are in imx8mp-power.h */
+	plat->subdomains = 5;
+
 	priv->base = dev_read_addr_ptr(dev);
 
 	ret = clk_get_by_name(dev, "usb", &priv->clk_usb);