scsi: ibmvscsis: Synchronize cmds at remove time

[ Upstream commit 8bf11557d44d00562360d370de8aa70ba89aa0d5 ]

This patch adds code to disconnect from the client, which will make sure
any outstanding commands have been completed, before continuing on with
the remove operation.

Signed-off-by: Michael Cyr <mikecyr@us.ibm.com>
Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Tested-by: Steven Royer <seroyer@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>