uprobes/x86: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
by explicitly adding a break statement instead of letting the code fall
through to the next case.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://github.com/KSPP/linux/issues/115

arch/x86/kernel/uprobes.c

@@ -1015,6 +1015,8 @@ int arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val,
 		if (uprobe_post_sstep_notifier(regs))
 			ret = NOTIFY_STOP;
 
+		break;
+
 	default:
 		break;
 	}