Later GCC compilers >=9 fail with a `this statement may fall through`
error due to this missing break.
Change-Id: I44b3386930a0b71b842a3a9b4837e4d6ad588f9d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31215
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>