shpchp: fix shpchp_wait_cmd in poll

This patch fixes the problem that issuing SHPC command in poll mode
always fails with the following message.

        shpchp: Command not completed in 2000 msec

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>