s390/cmm: use string_upper() instead of open coded variant

Use string_upper() from string helper module instead of open coded variant.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211001130201.72545-1-andriy.shevchenko@linux.intel.com
[hca@linux.ibm.com: removed hunk which converts extmem.c]
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/mm/cmm.c

@@ -14,8 +14,8 @@
 #include <linux/moduleparam.h>
 #include <linux/gfp.h>
 #include <linux/sched.h>
+#include <linux/string_helpers.h>
 #include <linux/sysctl.h>
-#include <linux/ctype.h>
 #include <linux/swap.h>
 #include <linux/kthread.h>
 #include <linux/oom.h>
@@ -394,13 +394,10 @@ static int __init cmm_init(void)
 		goto out_sysctl;
 #ifdef CONFIG_CMM_IUCV
 	/* convert sender to uppercase characters */
-	if (sender) {
-		int len = strlen(sender);
-		while (len--)
-			sender[len] = toupper(sender[len]);
-	} else {
+	if (sender)
+		string_upper(sender, sender);
+	else
 		sender = cmm_default_sender;
-	}
 
 	rc = smsg_register_callback(SMSG_PREFIX, cmm_smsg_target);
 	if (rc < 0)