log: don't kill mtrace if we haven't started one

If a '-s 0' flag is used when starting tests to disable firmware
logging, the logger shouldn't be killed either. Use a correct test
for this.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

Author: lyakh

case-lib/hijack.sh

@@ -92,7 +92,7 @@ function func_exit_handler()
 
     fi
 
-    if [ "$SOF_LOGGING" != 'none' ] && is_ipc4 && is_firmware_file_zephyr; then
+    if ! logger_disabled && is_ipc4 && is_firmware_file_zephyr; then
         local mtraceBin; mtraceBin=mtrace-reader.py
         dlogi "pkill -TERM -f $mtraceBin"
         sudo pkill -TERM -f "$mtraceBin" || {