s390/extable: search amode31 extable last

It is very unlikely that an exception happens within the amode31 text
section, therefore safe a couple of cycles for the common case, and
search the amode31 extable last.
Reviewed-by: NAlexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: NHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>

arch/s390/mm/fault.c

@@ -230,13 +230,13 @@ static noinline void do_sigsegv(struct pt_regs *regs, int si_code)
 const struct exception_table_entry *s390_search_extables(unsigned long addr)
 {
 	const struct exception_table_entry *fixup;
+	size_t num;
 
-	fixup = search_extable(__start_amode31_ex_table,
-			       __stop_amode31_ex_table - __start_amode31_ex_table,
-			       addr);
-	if (!fixup)
-		fixup = search_exception_tables(addr);
-	return fixup;
+	fixup = search_exception_tables(addr);
+	if (fixup)
+		return fixup;
+	num = __stop_amode31_ex_table - __start_amode31_ex_table;
+	return search_extable(__start_amode31_ex_table, num, addr);
 }
 
 static noinline void do_no_context(struct pt_regs *regs)