tar: add missing hash for host variant

This fixes a very early error in a fresh build:
"ERROR: No hash found for tar-1.28.cpio.gz"

[Thomas: adjust commit title.]

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

package/tar/tar.hash

@@ -1,2 +1,3 @@
 # Locally calculated after checking signature
 sha256	64ee8d88ec1b47a0961033493f919d27218c41b580138fd6802327462aff22f2	tar-1.28.tar.xz
+sha256	a3906a862f83dac1dfaf0ed200c62bd21f6d00f184a7f42b91978593a8553104	tar-1.28.cpio.gz