stats: Add M5_VAR_USED to variable

Fixes compile error for gem5.fast due to unused variable.

Change-Id: Ib1664b100e95a741174610f8cdbdebaff9635f66
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20759
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed