Fix "set but not used" in smartpqi. The PCI_MEM macros don't require a
physical/absolute address in FreeBSD, but it looks like the calling
code might be somewhat portable to other OS's that do require this.
Therefore, set the variables to __unused instead of removing the code
entirely.

(cherry picked from commit e28289ca83673d753b7e479810947f6a1015ad39)