Bluetooth: HCI: Fix definition of hci_rp_read_stored_link_key

Both max_num_keys and num_key are 2 octects:

BLUETOOTH CORE SPECIFICATION Version 5.3 | Vol 4, Part E
page 1985:

  Max_Num_Keys:
  Size: 2 octets
  Range: 0x0000 to 0xFFFF

  Num_Keys_Read:
  Size: 2 octets
  Range: 0x0000 to 0xFFFF

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>