perf buildid-cache: Update help text for purge command

Clarify the perf buildid-cache help text for the purge operation.  The
purge subcommand takes a list of files (binaries) as option parameter.
Make the wording the same as for the add and remove operation.

Signed-off-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
LPU-Reference: 20171107144853.12925-1-tmricht@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-buildid-cache.c

@@ -325,8 +325,8 @@ int cmd_buildid_cache(int argc, const char **argv)
 		   "file", "kcore file to add"),
 	OPT_STRING('r', "remove", &remove_name_list_str, "file list",
 		    "file(s) to remove"),
-	OPT_STRING('p', "purge", &purge_name_list_str, "path list",
-		    "path(s) to remove (remove old caches too)"),
+	OPT_STRING('p', "purge", &purge_name_list_str, "file list",
+		    "file(s) to remove (remove old caches too)"),
 	OPT_STRING('M', "missing", &missing_filename, "file",
 		   "to find missing build ids in the cache"),
 	OPT_BOOLEAN('f', "force", &force, "don't complain, do it"),