pkg-download: VERIFY_HASH: use same hash file for host and target downloads

Fixes (or atleast stops the build with a saner description):
http://autobuild.buildroot.net/results/1a9/1a9643f8633db038d4fe5ca4a32e4d52e70a3a1a/



We're using the same sources for host and target downloads, so it makes
sense to use the same <pkg>.hash file as well to ensure the host version
gets verified without us having to maintain a seperate host-<pkg>.hash file.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>