shpchp: remove unnecessary cmd_busy member from struct controller

This patch removes unnecessary cmd_busy member from struct
controller. Read command status register instead of using cmd_busy.

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>