Makefile: clean block-sha1/ directory instead of mozilla-sha1/

'make clean' should remove the object files from block-sha1/
instead of the non-existent mozilla-sha1/ directory.
Signed-off-by: NCarlos R. Mafra <crmafra@aei.mpg.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Makefile

@@ -1827,7 +1827,7 @@ distclean: clean
 	$(RM) configure
 
 clean:
-	$(RM) *.o mozilla-sha1/*.o arm/*.o ppc/*.o compat/*.o compat/*/*.o xdiff/*.o \
+	$(RM) *.o block-sha1/*.o arm/*.o ppc/*.o compat/*.o compat/*/*.o xdiff/*.o \
 		$(LIB_FILE) $(XDIFF_LIB)
 	$(RM) $(ALL_PROGRAMS) $(BUILT_INS) git$X
 	$(RM) $(TEST_PROGRAMS)