pciehp: fix wait command completion

This patch fixes this problem that pciehp driver will sleep
unnecessarily long when waiting for command completion. With this
patch, modprobe pciehp driver becomes very faster as follows for
instance.

  o Without this patch
    # time /sbin/modprobe pciehp

    real    0m4.976s
    user    0m0.000s
    sys     0m0.004s

  o With this patch
    # time /sbin/modprobe pciehp

    real    0m0.640s
    user    0m0.000s
    sys     0m0.004s

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>