kernel/wr_pstats: get rid of undefined function warning

get rid of warning:
WARNING: "wr_nic_pstats_callback" [/home/awujek/wrs/wr-switch-sw/kernel/wr_pstats/wr_pstats.ko] undefined!

Signed-off-by: Adam Wujek <adam.wujek@cern.ch>

kernel/wr_pstats/Makefile

@@ -8,5 +8,5 @@ all modules:
 	$(MAKE) -C $(LINUX) SUBDIRS=$(shell /bin/pwd) modules
 
 clean:
-	rm -f *.mod.c *.o *.ko *.i .*cmd Module.symvers modules.order *~
+	rm -f *.mod.c *.o *.ko *.i .*cmd  modules.order *~
 	rm -rf .tmp_versions

kernel/wr_pstats/Module.symvers

+0x00000000	wr_nic_pstats_callback	/home/awujek/wrs/wr-switch-sw/kernel/wr_nic/wr-nic	EXPORT_SYMBOL