clk: mxl: syscon_node_to_regmap() returns error pointers

Commit 03617731 ("clk: mxl: Switch from direct readl/writel based IO
to regmap based IO") introduced code resulting in below warning issued
by the smatch static checker.

  drivers/clk/x86/clk-lgm.c:441 lgm_cgu_probe() warn: passing zero to 'PTR_ERR'

Fix the warning by replacing incorrect IS_ERR_OR_NULL() with IS_ERR().

Fixes: 03617731 ("clk: mxl: Switch from direct readl/writel based IO to regmap based IO")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rahul Tanwar <rtanwar@maxlinear.com>
Link: https://lore.kernel.org/r/49e339d4739e4ae4c92b00c1b2918af0755d4122.1666695221.git.rtanwar@maxlinear.comSigned-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/x86/clk-lgm.c

@@ -436,7 +436,7 @@ static int lgm_cgu_probe(struct platform_device *pdev)
 	ctx->clk_data.num = CLK_NR_CLKS;
 
 	ctx->membase = syscon_node_to_regmap(np);
-	if (IS_ERR_OR_NULL(ctx->membase)) {
+	if (IS_ERR(ctx->membase)) {
 		dev_err(dev, "Failed to get clk CGU iomem\n");
 		return PTR_ERR(ctx->membase);
 	}