printk: fix invalid-free on devkmsg_write()

Now buf is allocated on stack and thus doesn't need to be freed.
This leftover would cause undefined behaviour.

Fixes: 9ec4ab41a8b5c ("printk: use buffer from the stack space")

Signed-off-by: xNombre <kartapolska@gmail.com>
Signed-off-by: Park Ju Hyung <qkrwngud825@gmail.com>
Signed-off-by: celtare21 <celtare21@gmail.com>
Signed-off-by: engstk <eng.stk@sapo.pt>

kernel/printk/printk.c

@@ -789,10 +789,8 @@ static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
 	}
 
 	buf[len] = '\0';
-	if (!copy_from_iter_full(buf, len, from)) {
-		kfree(buf);
+	if (!copy_from_iter_full(buf, len, from))
 		return -EFAULT;
-	}
 
 	/*
 	 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace