mailbox: imx: fix crash in resume on i.mx8ulp

check 'priv->clk' before 'imx_mu_read()' otherwise crash happens on
i.mx8ulp, since clock not enabled.

Fixes: 4f0b776 ("mailbox: imx-mailbox: support i.MX8ULP MU")
Reviewed-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/imx-mailbox.c

@@ -725,7 +725,7 @@ static int __maybe_unused imx_mu_resume_noirq(struct device *dev)
 	 * send failed, may lead to system freeze. This issue
 	 * is observed by testing freeze mode suspend.
 	 */
-	if (!imx_mu_read(priv, priv->dcfg->xCR[0]) && !priv->clk) {
+	if (!priv->clk && !imx_mu_read(priv, priv->dcfg->xCR[0])) {
 		for (i = 0; i < IMX_MU_xCR_MAX; i++)
 			imx_mu_write(priv, priv->xcr[i], priv->dcfg->xCR[i]);
 	}