Fix various kernel warnings.

src/acpi/aml/namespace.rs

src/acpi/dmar/mod.rs

src/acpi/fadt.rs

src/acpi/hpet.rs

src/acpi/madt.rs

src/acpi/mod.rs

src/acpi/rsdt.rs

src/acpi/rxsdt.rs

src/acpi/xsdt.rs

src/arch/x86_64/device/ioapic.rs

src/arch/x86_64/device/mod.rs

src/arch/x86_64/interrupt/irq.rs

src/arch/x86_64/start.rs

src/scheme/acpi.rs

src/scheme/irq.rs

src/scheme/serio.rs

src/syscall/process.rs