Makefile: Fix generating RPM log during bumpver

We stopped using the release version in tags in 07352e9 so we
need to use the correct tag when getting log for RPM changelog.

Makefile.am

@@ -172,8 +172,8 @@ tag:
 
 rpmlog:
 	@cl=`grep -n %changelog dist/libblockdev.spec.in |cut -d : -f 1 |head -1` ; \
-	version_release=`tail --lines=+$$(($$cl + 1)) dist/libblockdev.spec.in|head -1|cut -d- -f2-3|sed 's/ //g'` ; \
-	git log --no-merges --pretty="format:- %s (%ae)" "$$version_release.." |sed -e 's/@.*)/)/' ; \
+	version=`tail --lines=+$$(($$cl + 1)) dist/libblockdev.spec.in|head -1|cut -d- -f2|sed 's/ //g'` ; \
+	git log --no-merges --pretty="format:- %s (%ae)" "$$version.." |sed -e 's/@.*)/)/' ; \
 	echo
 
 shortlog: