Makefile: Fix tag file generation targets

"ctags" produces a file named "tags", not "ctags". It doesn't look
reasonable to use phony target name as a file name to remove. Just use
exact file names to remove in "ctags" and "TAGS" target receipts.
Signed-off-by: NSergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: NSergey Fedorov <sergey.fedorov@linaro.org>
Message-Id: <1465495115-24665-1-git-send-email-sergey.fedorov@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -498,12 +498,12 @@ test speed: all
 
 .PHONY: ctags
 ctags:
-	rm -f $@
+	rm -f tags
 	find "$(SRC_PATH)" -name '*.[hc]' -exec ctags --append {} +
 
 .PHONY: TAGS
 TAGS:
-	rm -f $@
+	rm -f TAGS
 	find "$(SRC_PATH)" -name '*.[hc]' -exec etags --append {} +
 
 cscope: