Remove const qualifier for the output argument

Payload with SMP_IO_CAP_REQ_EVT event has output arguments but
tSMP_EVT_DATA is declared a const in tSMP_CALLBACK.

Test: mmm packages/modules/Bluetooth
Flag: EXEMPT refactor
Bug: 286334644
Change-Id: If72ecdbc1abdcb9957fcedcd268046bbb51fff71