base: Add an "override" to name() in the HardBreakpoint class.

clang reports an error otherwise and fails to compile.

Change-Id: I3603d6c710641f1289e35c67f89a49f5cb71e95e
Reviewed-on: https://gem5-review.googlesource.com/7582
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>