arm: Add a missing "break" in an ARM miscreg decode function.

arm: Add a missing "break" in an ARM miscreg decode function.

This change accidentally left out a "break" which gcc found and
complained about.

arch-arm: Implementation of Hardware Breakpoint exception

This change adds in the break based on the assumption that the function
should not fall through that case to the next.

Change-Id: Id728a0c9a504d1b6d231d3fe1e7c5ece05d3ac4d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30654
Reviewed-by: Jordi Vaquero <jordi.vaquero@metempsy.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>