lib/oe/sstatesig: Fix task mappings from multilib<->non-multilib contexts
If we're in a multilib context already and want a non-multilib context
this function returned incorrect values.
Try and retain optimisations for the common case not needing to request
a datastore but allow the different multilib/non-multilib combinations
to work too.
This fixes bugs where rootfs generation of a multilib image would
write into incorrect locations, or be unable to find sstate manifest
files due to incorrect data stores being used to expand data.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
