ext_man: Fix memory leak after manifest build

sec_buffer allocated inside elf_read_section()
was not being freed before and is freed now.

Signed-off-by: Karol Trzcinski <karolx.trzcinski@linux.intel.com>

src/ext_manifest.c

@@ -130,6 +130,7 @@ static int ext_man_build(const struct module *module,
 	*dst_buff = (struct ext_man_header *)buffer;
 
 out:
+	free(sec_buffer);
 	return ret;
 }