s390: Change s390_kernel_write() return type to match memcpy()

s390_kernel_write()'s function type is almost identical to memcpy().
Change its return type to "void *" so they can be used interchangeably.

Cc: linux-s390@vger.kernel.org
Cc: heiko.carstens@de.ibm.com
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> # s390
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

arch/s390/include/asm/uaccess.h

@@ -276,6 +276,6 @@ static inline unsigned long __must_check clear_user(void __user *to, unsigned lo
 }
 
 int copy_to_user_real(void __user *dest, void *src, unsigned long count);
-void s390_kernel_write(void *dst, const void *src, size_t size);
+void *s390_kernel_write(void *dst, const void *src, size_t size);
 
 #endif /* __S390_UACCESS_H */

arch/s390/mm/maccess.c

@@ -55,19 +55,22 @@ static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t siz
  */
 static DEFINE_SPINLOCK(s390_kernel_write_lock);
 
-void notrace s390_kernel_write(void *dst, const void *src, size_t size)
+notrace void *s390_kernel_write(void *dst, const void *src, size_t size)
 {
+	void *tmp = dst;
 	unsigned long flags;
 	long copied;
 
 	spin_lock_irqsave(&s390_kernel_write_lock, flags);
 	while (size) {
-		copied = s390_kernel_write_odd(dst, src, size);
-		dst += copied;
+		copied = s390_kernel_write_odd(tmp, src, size);
+		tmp += copied;
 		src += copied;
 		size -= copied;
 	}
 	spin_unlock_irqrestore(&s390_kernel_write_lock, flags);
+
+	return dst;
 }
 
 static int __no_sanitize_address __memcpy_real(void *dest, void *src, size_t count)