target: tcm_loop: Delete two unnecessary variable initialisations in tcm_loop_issue_tmr()

The variables "se_cmd" and "tl_cmd" will eventually be set to appropriate
pointers a bit later.
Thus omit the explicit initialisation at the beginning.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>