http://dl.ivtvdriver.org/${PN}/${P}.tar.gz should now be: http://dl.ivtvdriver.org/${PN}/unstable/${P}.tar.gz
It appears that now 0.4.0 has been released (see http://dl.ivtvdriver.org/ivtv/stable/ and http://dl.ivtvdriver.org/ivtv/unstable/readme.txt), 0.3.8 has been removed from http://dl.ivtvdriver.org/ivtv/unstable/.
0.4.0 is in the tree.