IB/qib: Fix txselect regression

Commit 7fac33014f54("IB/qib: checkpatch fixes") was overzealous in
removing a simple_strtoul for a parse routine, setup_txselect().  That
routine is required to handle a multi-value string.

Unwind that aspect of the fix.

Cc: <stable@vger.kernel.org>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>