configure.ac: fix polarssl autodetection

configure.ac: fix polarssl autodetection

A missing , in the previous configure.ac patch caused the autodetection to
fail.  While fixing that, I noticed I can simplify the check by using the
documented ${ac_cv_search_function} cache variable instead of the nested
AC_SEARCH_LIBS.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1453150181-21453-1-git-send-email-steffan@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/11010
Signed-off-by: Gert Doering <gert@greenie.muc.de>