system/irtest/Make.defs: fixed the wrong path

fix this error
make[3] *** /nuttxspace/nuttx/apps/testing/irtest: No such file or directory.  Stop.

error due to this change
apps/testing: Move irtest/sensortest/resmonitor/monkey to apps/system #2976

Signed-off-by: simbit18 <simbit18@gmail.com>

Author: simbit18

system/irtest/Make.defs

@@ -21,5 +21,5 @@
 ############################################################################
 
 ifneq ($(CONFIG_SYSTEM_IRTEST),)
-CONFIGURED_APPS += $(APPDIR)/testing/irtest
+CONFIGURED_APPS += $(APPDIR)/system/irtest
 endif