Fix to retrieve libva version.

Fixes #41

Signed-off-by: Lim Siew Hoon <siew.hoon.lim@intel.com>
(cherry picked from commit 780b91ef32ca218220918d111f0640cb6a2f3379)
diff --git a/configure.ac b/configure.ac
index e44d283..d467a4e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -138,6 +138,7 @@
 # Check for libva (for dynamic linking)
 LIBVA_API_MIN_VERSION=libva_api_min_version
 PKG_CHECK_MODULES([LIBVA], [libva >= $LIBVA_API_MIN_VERSION])
+LIBVA_VERSION=`$PKG_CONFIG --variable=libva_version libva`
 AC_SUBST(LIBVA_VERSION)
 LIBVA_API_VERSION=`$PKG_CONFIG --modversion libva`
 VA_MAJOR_VERSION=`echo "$LIBVA_API_VERSION" | cut -d'.' -f1`