qmempool: More cleanup and only reload cpu ptr when needed

In __qmempool_free(), only reload the percpu ptr, in case preempt
got reenabled, caused by the __qmempool_free_to_sharedq() needing
to access the real SLAB.

This also removes a debug pr_err() statement, that could be a
problem/too-loud for real use-cases.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>