[S390] memory detection: fix off by one bug.

diag 260 returns the address of the last addressable byte and not the
size of memory. Since we want the size we have to add 1 to the return
value.
Disable diag 260 for non z/Arch mode since it doesn't work there
anyway.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/early.c

@@ -141,9 +141,9 @@ static noinline __init void detect_machine_type(void)
 		machine_flags |= 4;
 }
 
+#ifdef CONFIG_64BIT
 static noinline __init int memory_fast_detect(void)
 {
-
 	unsigned long val0 = 0;
 	unsigned long val1 = 0xc;
 	int ret = -ENOSYS;
@@ -161,9 +161,15 @@ static noinline __init int memory_fast_detect(void)
 	if (ret || val0 != val1)
 		return -ENOSYS;
 
-	memory_chunk[0].size = val0;
+	memory_chunk[0].size = val0 + 1;
 	return 0;
 }
+#else
+static inline int memory_fast_detect(void)
+{
+	return -ENOSYS;
+}
+#endif
 
 #define ADDR2G	(1UL << 31)