[S390] bss section clearing.

Clear only memory from __bss_start to __bss_stop when clearing the bss
section. Not until _end, which currently happens to be the same.
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/early.c

@@ -110,7 +110,7 @@ static inline void create_kernel_nss(void) { }
  */
 static noinline __init void clear_bss_section(void)
 {
-	memset(__bss_start, 0, _end - __bss_start);
+	memset(__bss_start, 0, __bss_stop - __bss_start);
 }
 
 /*