hikey9xx: Fixed incorrect use of kfree to free sreg

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6GS86
CVE: NA

--------------------------------

When memory allocated by using the devm_kmalloc(). the matching
release function should use the devm_kfree() function instead of
the kfree() function.

@sreg allocated:
hi6421_spmi_regulator_probe
  hi6421_spmi_regulator_probe_ldo

@sreg freed:
hi6421_spmi_regulator_remove
Signed-off-by: NZhaoLong Wang <wangzhaolong1@huawei.com>
(cherry picked from commit 8a31aa41)

drivers/staging/hikey9xx/hi6421v600-regulator.c

@@ -452,7 +452,7 @@ static int hi6421_spmi_regulator_remove(struct platform_device *pdev)
 	if (rdev->desc->volt_table)
 		devm_kfree(&pdev->dev, (unsigned int *)rdev->desc->volt_table);
 
-	kfree(sreg);
+	devm_kfree(&pdev->dev, sreg);
 
 	return 0;
 }