[PATCH] shpchp - bugfix: add missing serialization

Current shpchp driver might cause system panic because of lack of
serialization. It can be reproduced very easily by the following
operation.

	# cd /sys/bus/pci/slots/<slot#>
	# while true; do echo 0 > power ; echo 1 > power ; done &
	# while true; do echo 0 > power ; echo 1 > power ; done &

This patch fixes this issue by changing shpchp to get appropreate
semaphore for hot-plug operation.

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