target: fix clang static analyzer warning

Removes Warning:	line 6482, column 12
1st function call argument is an uninitialized value

Use target ptr directly as checked in previous lines instead of
dereferencing head->target

Change-Id: I6804b776fd493af71f3098d702f9cdc7acb50151
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/6970
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/target.c

@@ -6477,7 +6477,7 @@ static int jim_target_smp(Jim_Interp *interp, int argc, Jim_Obj *const *argv)
 	}
 
 	if (target && target->rtos)
-		retval = rtos_smp_init(head->target);
+		retval = rtos_smp_init(target);
 
 	return retval;
 }