build: fix enable/disable language in ./configure --help

Based on patch from Brian Paul.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=32317
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
diff --git a/configure.ac b/configure.ac
index 9a3fde1..6a7521f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -877,7 +877,7 @@
 esac
 AC_ARG_ENABLE([driglx-direct],
     [AS_HELP_STRING([--disable-driglx-direct],
-        [enable direct rendering in GLX and EGL for DRI \
+        [disable direct rendering in GLX and EGL for DRI \
             @<:@default=auto@:>@])],
     [driglx_direct="$enableval"],
     [driglx_direct="$driglx_direct_default"])