xtensa: fix incorrect fd close in error case of simdisk_setup()

dev->fd is opened in attach operation, so should not
close dev->fd in error case of simdisk_setup().

Signed-off-by: Chengguang Xu <cgxu519@gmail.com>
Message-Id: <1557066367-4783-1-git-send-email-cgxu519@gmail.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>