thermal: imx8mm: Print the correct error code

Currently the error message does not print the correct error code.

Fix it by initializing 'ret' to the proper error code.

REFERENCE:
https://git.toradex.com/cgit/linux-toradex.git/commit/drivers/thermal/imx8mm_thermal.c?h=toradex_5.15-2.2.x-imx&id=ce662ccde5c6ae4f4d89fe71570bf59441004eb9

drivers/thermal/imx8mm_thermal.c

@@ -217,10 +217,11 @@ static int imx8mm_tmu_probe(struct platform_device *pdev)
 							     &tmu->sensors[i],
 							     &tmu_tz_ops);
 		if (IS_ERR(tmu->sensors[i].tzd)) {
+			ret = PTR_ERR(tmu->sensors[i].tzd);
 			dev_err(&pdev->dev,
 				"failed to register thermal zone sensor[%d]: %d\n",
 				i, ret);
-			return PTR_ERR(tmu->sensors[i].tzd);
+			return ret;
 		}
 		tmu->sensors[i].hw_id = i;