[gn][banjo] Fix warning in MakeSquiggle()

gn build has fallthrough warnings enabled; looks like this was intending
to be a break.

ZX-3415 #comment [gn][banjo] Fix warning in MakeSquiggle()

Test: CQ
Change-Id: Ica96133a14896c2a647b7769bf645a8f7523e74a
diff --git a/zircon/system/host/banjo/lib/error_reporter.cpp b/zircon/system/host/banjo/lib/error_reporter.cpp
index cd55ccf..d93d624 100644
--- a/zircon/system/host/banjo/lib/error_reporter.cpp
+++ b/zircon/system/host/banjo/lib/error_reporter.cpp
@@ -15,6 +15,7 @@
         switch (surrounding_line[i]) {
         case '\t':
             squiggle.push_back('\t');
+            break;
         default:
             squiggle.push_back(' ');
         }