soc: imx8m: Fix incorrect check for of_clk_get_by_name()

of_clk_get_by_name() returns error pointers instead of NULL.
Use IS_ERR() checks the return value to catch errors.

Fixes: 836fb30949 ("soc: imx8m: Enable OCOTP clock before reading the register")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

drivers/soc/imx/soc-imx8m.c

@@ -66,8 +66,8 @@ static u32 __init imx8mq_soc_revision(void)
 	ocotp_base = of_iomap(np, 0);
 	WARN_ON(!ocotp_base);
 	clk = of_clk_get_by_name(np, NULL);
-	if (!clk) {
-		WARN_ON(!clk);
+	if (IS_ERR(clk)) {
+		WARN_ON(IS_ERR(clk));
 		return 0;
 	}