Bluetooth: fix err_cast.cocci warnings

net/bluetooth/smp.c:2650:9-16: WARNING: ERR_CAST can be used with tfm_aes

Use ERR_CAST inlined function instead of ERR_PTR(PTR_ERR(...))

Generated by: scripts/coccinelle/api/err_cast.cocci

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>