luarocks-package: use $(HOST_PKG_VERSION) instead of $(PKG_VERSION)

luarocks-package: use $(HOST_PKG_VERSION) instead of $(PKG_VERSION)

The inner-luarocks-package macro was using $(3)_VERSION as the package
version, i.e. the version of the target package, even when it's the
host package. We should instead use $(2)_VERSION, i.e. the host package
version, like is done in inner-generic-package.

Since luarocks-package doesn't even support a host version, it doens't
make a whole lot of difference, but let's keep things consistent.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>