[x86] remove uses of magic macros for boot_params access

Instead of using magic macros for boot_params access, simply use the
boot_params structure.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/drivers/lguest/lguest.c b/drivers/lguest/lguest.c
index ee1c6d0..4a579c8 100644
--- a/drivers/lguest/lguest.c
+++ b/drivers/lguest/lguest.c
@@ -893,7 +893,9 @@
 
 	/* The Linux bootloader header contains an "e820" memory map: the
 	 * Launcher populated the first entry with our memory limit. */
-	add_memory_region(E820_MAP->addr, E820_MAP->size, E820_MAP->type);
+	add_memory_region(boot_params.e820_map[0].addr,
+			  boot_params.e820_map[0].size,
+			  boot_params.e820_map[0].type);
 
 	/* This string is for the boot messages. */
 	return "LGUEST";