rust/irq: Add a helper to convert [InterruptSource] to pointer This is useful when taking an InterruptSource slice and passing it to C function. Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Zhao Liu <zhao1.liu@intel.com> Link: https://lore.kernel.org/r/20250210030051.2562726-4-zhao1.liu@intel.com Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>