coreboot: don't return struct lb_memory * from write_tables()

No one is interrogating the write_tables() return value. Therefore,
drop it.

Change-Id: I97e707f071942239c9a0fa0914af3679ee7a9c3c
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/5301
Tested-by: build bot (Jenkins)
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>

src/include/boot/tables.h

@@ -3,6 +3,6 @@
 
 #include <boot/coreboot_tables.h>
 
-struct lb_memory *write_tables(void);
+void write_tables(void);
 
 #endif /* BOOT_TABLES_H */