builtin/diff.c: remove duplicated call to diff_result_code()

The return value from builtin_diff_files() is fed to diff_result_code()
by the caller, and all other callees like builtin_diff_index() do not
have their own call to diff_result_code().  Remove the duplicated one
from builtin_diff_files() and let the caller handle it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/diff.c

@@ -207,7 +207,6 @@ static void refresh_index_quietly(void)
 
 static int builtin_diff_files(struct rev_info *revs, int argc, const char **argv)
 {
-	int result;
 	unsigned int options = 0;
 
 	while (1 < argc && argv[1][0] == '-') {
@@ -241,8 +240,7 @@ static int builtin_diff_files(struct rev_info *revs, int argc, const char **argv
 		perror("read_cache_preload");
 		return -1;
 	}
-	result = run_diff_files(revs, options);
-	return diff_result_code(&revs->diffopt, result);
+	return run_diff_files(revs, options);
 }
 
 int cmd_diff(int argc, const char **argv, const char *prefix)