mkimage: Fix missing free() in fit_extract_data()

The 'buf' variable is not freed. Fix it.

Reported-by: Coverity (CID: 138492)
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

tools/fit_image.c

@@ -452,6 +452,8 @@ static int fit_extract_data(struct image_tool_params *params, const char *fname)
 err_munmap:
 	munmap(fdt, sbuf.st_size);
 err:
+	if (buf)
+		free(buf);
 	close(fd);
 	return ret;
 }