IB/hfi1: Do not override given pcie_pset value

During PCIe Gen 3 transistion, pcie_pset is read and might be overridden
to a default value(i.e. 255) in do_pcie_gen3_transition() routine.

If the pcie_pset value is overridden then this new value will be used
during initialization of next adapter on a different card.

Introducing a new local variable to avoid modification of pcie_pset

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Bartlomiej Dudek <bartlomiej.dudek@intel.com>
Signed-off-by: Patel Jay P <jay.p.patel@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>