bootstrap: Escape mirrors

When we have mirrors set to $(CT_Mirror foo bar) we need some extra
escaping so that they get interpreted correctly by kconfig.

Signed-off-by: Chris Packham <judge.packham@gmail.com>

bootstrap

@@ -596,6 +596,8 @@ enter_fork()
         info[repository_url]=${info[repository]#* }
     fi
 
+    info[mirrors]=${info[mirrors]//$\(/\\$\(}
+
     versions=`cd packages/${fork} && \
         for f in */version.desc; do [ -r "${f}" ] && echo "${f%/version.desc}"; done`
     versions=`sort_versions ${versions}`