classes/create-spdx-2.2: Use hashfn from BB_TASKDEPDATA instead of MACHINE

classes/create-spdx-2.2: Use hashfn from BB_TASKDEPDATA instead of MACHINE

Enabling the SPDX class and running two builds, one with SDKMACHINE=i686
and then again with SDKMACHINE=x86_64 would lead to errors since the output
was stored per MACHINE and the overlapping files would cause manifest errors.

The hashfn data from bitbake has SSTATE_PKGARCH encoded into it which is how
sstate separates out it's targets and SDPX should be using the same structure.
Therefore switch to using this.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>