Switch to new stack when calling ATA function in 16bit mode.

This reduces stack usage (old dos programs don't provide much space).
diff --git a/src/asm-offsets.c b/src/asm-offsets.c
index 1e3a293..c3c3bc6 100644
--- a/src/asm-offsets.c
+++ b/src/asm-offsets.c
@@ -25,7 +25,5 @@
     OFFSET(BDA_ebda_seg, bios_data_area_s, ebda_seg);
 
     COMMENT("EBDA");
-    OFFSET(EBDA_resume_stack_top, extended_bios_data_area_s
-           , resume_stack[FIELD_SIZEOF(struct extended_bios_data_area_s
-                                       , resume_stack)]);
+    DEFINE(EBDA_OFFSET_TOP_STACK, EBDA_OFFSET_TOP_STACK);
 }