[SCSI] zfcp: Merge FCP task management setup with regular FCP command setup

For task management commands, only LUN and flags are required. The
regular FCP setup already sets the LUN in the fcp_cmnd. All is
required for merging the function is setting up the TM flags.

Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>