x86, boot: correct the calculation of ZO_INIT_SIZE

Correct the calculation of ZO_INIT_SIZE (the amount of memory we need
during decompression).  One symbol (ZO_startup_32) was missing from
zoffset.h, and another (ZO_z_extract_offset) was misspelled.

[ Impact: build fix ]

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 68c3bfb..1040f6e 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -226,7 +226,7 @@
 
 pref_address:		.quad LOAD_PHYSICAL_ADDR	# preferred load addr
 
-#define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_extract_offset)
+#define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_z_extract_offset)
 #define VO_INIT_SIZE	(VO__end - VO__text)
 #if ZO_INIT_SIZE > VO_INIT_SIZE
 #define INIT_SIZE ZO_INIT_SIZE