eigen: use mercurial tag

Now that our Mercurial download mechanism has been fixed to also
support tags, let's use this possibility in the eigen package.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/eigen/eigen.mk

@@ -4,8 +4,7 @@
 #
 ################################################################################
 
-# version 3.2.5
-EIGEN_VERSION = 175a47a35f0c
+EIGEN_VERSION = 3.2.5
 EIGEN_SITE = https://bitbucket.org/eigen/eigen
 EIGEN_SITE_METHOD = hg
 EIGEN_LICENSE = MPL2, BSD-3c, LGPLv2.1