flashtool: Fix compile error due to missing statement after default label

In flashtool_main.c, the 'default:' label in a switch statement was
followed directly by '}', which is invalid in C.
This commit adds a 'break;' statement after the default label to
resolve the error.

Signed-off-by: tuansuper <tunainnet@tutanota.com>

fsutils/flashtool/flashtool_main.c

@@ -365,6 +365,7 @@ int main(int argc, FAR char *argv[])
         ret = check_bad_block(fd, &geo);
         break;
       default:
+        break;
     }
 
 oops: