[PATCH] shpchp: fix improper reference to Slot Avail Regsister

The hpc_get_max_bus_speed() function of the SHPCHP driver seems to
refer wrong bits in the "Slot Avail Register I" and "Slot Avail
Register II". This patch fixes this bug. And this also cleanup the
code.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>