vfs_fruit: factor out common code from ad_get() and ad_fget()

vfs_fruit: factor out common code from ad_get() and ad_fget()

As a result of the previous changes ad_get() and ad_fget() do completey
the same, so factor out the common code to a new helper function. No
change in behaviour.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=12791

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Richard Sharpe <realrichardsharpe@gmail.com>
Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Wed Aug  9 22:33:36 CEST 2017 on sn-devel-144

(backported from commit d55c27abc5a7357f740c7065bbe12e7f36b57125)

Autobuild-User(v4-5-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-5-test): Mon Aug 14 14:52:17 CEST 2017 on sn-devel-144