arch/x86/tables.c: Avoid static analysis error for unused value

Within procedure arch_write_tables, the pointer "rom_table_end" is updated
every time a table is created. However, after creating last table, pointer
rom_table_end is not used, though it is updated. Add a "(void)rom_table_end;"
at the end to avoid the static analysis error.

BUG=b:112253891
TEST=Build and boot grunt.

Change-Id: I8a34026795c7f0d1bb86c5f5c0469d40aa53994a
Signed-off-by: Richard Spiegel <richard.spiegel@silverbackltd.com>
Reviewed-on: https://review.coreboot.org/27958
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/arch/x86/tables.c

@@ -259,6 +259,9 @@ void arch_write_tables(uintptr_t coreboot_table)
 	forwarding_table += sz;
 	/* Align up to page boundary for historical consistency. */
 	forwarding_table = ALIGN_UP(forwarding_table, 4*KiB);
+
+	/* Tell static analysis we know value is left unused. */
+	(void)rom_table_end;
 }
 
 void bootmem_arch_add_ranges(void)