target/arm: Add missing break statement for Hypervisor Trap Exception

target/arm: Add missing break statement for Hypervisor Trap Exception

Reported by GCC9 when building with  -Wimplicit-fallthrough=2:

  target/arm/helper.c: In function ‘arm_cpu_do_interrupt_aarch32_hyp’:
  target/arm/helper.c:7958:14: error: this statement may fall through [-Werror=implicit-fallthrough=]
   7958 |         addr = 0x14;
        |         ~~~~~^~~~~~
  target/arm/helper.c:7959:5: note: here
   7959 |     default:
        |     ^~~~~~~
  cc1: all warnings being treated as errors

Fixes: b9bc21ff9f9
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Reported-by: Stefan Weil <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Message-id: 20190719111451[email protected]
Signed-off-by: Peter Maydell <[email protected]>