acpi_spmc: Fix checking expected DSMs

Previously was or'ing the indices of the DSMs directly, not their
corresponding bits. This commit rectifies this.

Reviewed by: olce
Approved by: olce
Fixes: c5daa5a4c32c ("acpi_spmc: Add system power management controller driver")
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/https://reviews.freebsd.org/D56062