Bluetooth: Fix missing rewrite `attr`

When call `bt_gatt_notify_cb` with param->attr set to null.
and attr->uuid set to given uuid, the internal notify will
search uuid, but not assigned to param->attr, which cauce
null point reference when:
   notify --> gatt_notify  --> bt_gatt_check_perm

Signed-off-by: Lingao Meng <menglingao@xiaomi.com>