perf Documentation: Fix out-of-tree asciidoctor man page generation

The dependency for the man page rule using asciidoctor incorrectly
specifies a source file in $(OUTPUT). When building out-of-tree, the
source file is not found, resulting in a fall-back to the following rule
which uses xmlto.

Signed-off-by: Ben Hutchings <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Fixes: ffef80ecf89f ("perf Documentation: Support for asciidoctor")
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/Makefile

···
 	mv $@+ $@
 
 ifdef USE_ASCIIDOCTOR
-$(OUTPUT)%.1 $(OUTPUT)%.5 $(OUTPUT)%.7 : $(OUTPUT)%.txt
+$(OUTPUT)%.1 $(OUTPUT)%.5 $(OUTPUT)%.7 : %.txt
 	$(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
 	$(ASCIIDOC) -b manpage -d manpage \
 		$(ASCIIDOC_EXTRA) -aperf_version=$(PERF_VERSION) -o $@+ $< && \