file: fix regression for determining DB file type

file: fix regression for determining DB file type

The version 5.33 introduced a regression bug for determining the DB file
type. Backport a patch from upstream to fix it.

Before apply the patch:
$ file aliases.db
aliases.db: created: Thu Jan  1 00:38:24 1970, modified: Thu Jan  1 00:00:00 1970

After apply the patch:
$ file aliases.db
aliases.db: Berkeley DB (Btree, version 9, native byte-order)

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>