IB/qib: Correct nfreectxts for multiple HCAs

IB/qib: Correct nfreectxts for multiple HCAs

The code that was recently introduced to report the number
of free contexts is flawed for multiple HCAs:

       /* Return the number of free user ports (contexts) available. */
       return scnprintf(buf, PAGE_SIZE, "%u\n", dd->cfgctxts -
                dd->first_user_ctxt - (u32)qib_stats.sps_ctxts);

The qib_stats is global to the module, not per HCA, so the code is broken
for multiple HCAs.

This patch adds a qib_devdata field, freectxts, that reflects the free
contexts for this HCA.

Signed-off-by: Mike Marciniszyn <[email protected]>
Reviewed-by: Ram Vepa <[email protected]>
Signed-off-by: Roland Dreier <[email protected]>