IB/qib: Use a single txselect module parameter for serdes tuning

As part of the earlier patches submitted and reviewed, it was agreed
to change the way serdes tuning parameters were specified to the
driver.  The updated patch got dropped by the linux-rdma email list so
the earlier version of qib_iba7322.c ended up being used.  This patch
updates qib_iab7322.c to the simpler, single parameter method of
setting the serdes parameters.

Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>