optionsrom: Reserve space for checksum

Always add a byte before the final 512-bytes alignment to reserve the
space for the ROM checksum.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

pc-bios/optionrom/optionrom.h

diff --git a/pc-bios/optionrom/optionrom.h b/pc-bios/optionrom/optionrom.h
index aa783de..3daf7da 100644
--- a/pc-bios/optionrom/optionrom.h
+++ b/pc-bios/optionrom/optionrom.h
@@ -124,7 +124,8 @@
 	movw		%ax, %ds;
 
 #define OPTION_ROM_END					\
-    .align 512, 0;					\
+	.byte		0;				\
+	.align		512, 0;				\
     _end:
 
 #define BOOT_ROM_END					\