remove incorrect flat_to_off16

Here we use offsetof so "start" is not a flat pointer, it is
a pointer inside the e820 segment.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/code16.c b/code16.c
index f933915..cfcf50a 100644
--- a/code16.c
+++ b/code16.c
@@ -57,7 +57,7 @@
 		unsigned int i;
 		uint8_t *p;
 
-		start	= flat_to_off16(offsetof(struct e820map, map[ndx]));
+		start	= offsetof(struct e820map, map[ndx]);
 
 		p	= (void *) regs->edi;