arch-riscv,misc: Added M5_VAR_USED to MiscRegNames

Clang compilers return an error about MiscRegNames being unused.
M5_VAR_USED fixes this.

Change-Id: I515c5d1e8837020b674de49039c0525f896b7e37
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/29452
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed