pciehp: Remove useless hotplug interrupt enabling

Hotplug interrupt is enabled at initialization and nobody clears it.
So we need to setup it in each command. This patch removes redundant
codes about this.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>