arch/x86/acpigen: Fix comment in _ROM method generator

Commit 24462e6507 ("x86/acpigen: Fix ACPI _ROM method") changed the code
to generate a serialized method, but didn't adjust the comment.

Change-Id: Ie7dbaff13d36f31e9d627609d0f74a4e9fa5a1e9
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/28591
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/arch/x86/acpigen.c

@@ -1453,7 +1453,7 @@ void acpigen_write_rom(void *bios, const size_t length)
 	ASSERT(bios)
 	ASSERT(length)
 
-	/* Method (_ROM, 2, NotSerialized) */
+	/* Method (_ROM, 2, Serialized) */
 	acpigen_write_method_serialized("_ROM", 2);
 
 	/* OperationRegion("ROMS", SYSTEMMEMORY, current, length) */