[gn][fidl] Fix minor bug in MakeSquiggle()

The upcoming zircon gn build is less lenient and checks fallthrough. It
looks like this was intended to be a break not a fallthrough.

ZX-3415 #comment [gn][fidl] Fix minor bug in MakeSquiggle()

Test: CQ
Change-Id: I3e424aa1e515bd53ea60ae209a4f2b1cfe025f18
diff --git a/zircon/system/host/fidl/lib/error_reporter.cpp b/zircon/system/host/fidl/lib/error_reporter.cpp
index fbd735b..0ad856a 100644
--- a/zircon/system/host/fidl/lib/error_reporter.cpp
+++ b/zircon/system/host/fidl/lib/error_reporter.cpp
@@ -15,6 +15,7 @@
         switch (surrounding_line[i]) {
         case '\t':
             squiggle.push_back('\t');
+            break;
         default:
             squiggle.push_back(' ');
         }