arm64: ptrace: Fix missing return in hw breakpoint code

When delivering a hw-breakpoint SIGTRAP to a compat task via ptrace, the
lack of a 'return' statement means we fallthrough to the native case,
which differs in its handling of 'si_errno'.

Although this looks to be harmless because the subsequent signal is
effectively ignored, it's confusing and unintentional, so add the
missing 'return'.

Signed-off-by: Keno Fischer <keno@juliacomputing.com>
Link: https://lore.kernel.org/r/20210202002109.GA624440@juliacomputing.com
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/ptrace.c

@@ -194,6 +194,7 @@ static void ptrace_hbptriggered(struct perf_event *bp,
 		}
 		arm64_force_sig_ptrace_errno_trap(si_errno, bkpt->trigger,
 						  desc);
+		return;
 	}
 #endif
 	arm64_force_sig_fault(SIGTRAP, TRAP_HWBKPT, bkpt->trigger, desc);