build-sys: use use ${ac_default_prefix}

diff --git a/configure.ac b/configure.ac
index 497a74fc0af188fbc6b56e09914f2024bfce20cc..4fc75a434ab3cecac5309a435fa6957f4518ea55 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -58,7 +58,7 @@ AC_SUBST(PCI_DATABASE)
 
 AC_ARG_WITH([rootprefix],
        AS_HELP_STRING([--with-rootprefix=DIR], [rootfs directory prefix for config files and kernel modules]),
-       [], [with_rootprefix=$prefix])
+       [], [with_rootprefix=${ac_default_prefix}])
 AC_SUBST([rootprefix], [$with_rootprefix])
 
 AC_ARG_WITH([rootlibdir],