Bluetooth: btrtl: fix out of bounds memory access

The problem is detected by KASAN.
btrtl driver uses private hci data to store 'struct btrealtek_data'.
If btrtl driver is used with btusb, then memory for private hci data
is allocated in btusb. But no private data is allocated after hci_dev,
when btrtl is used with hci_h5.

This commit adds memory allocation for hci_h5 case.

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 BUG: KASAN: slab-out-of-bounds in btrtl_initialize+0x6cc/0x958 [btrtl]
 Write of size 8 at addr ffff00000f5a5748 by task kworker/u9:0/76

 Hardware name: Pine64 PinePhone (1.2) (DT)
 Workqueue: hci0 hci_power_on [bluetooth]
 Call trace:
  dump_backtrace+0x9c/0x128
  show_stack+0x20/0x38
  dump_stack_lvl+0x48/0x60
  print_report+0xf8/0x5d8
  kasan_report+0x90/0xd0
  __asan_store8+0x9c/0xc0
  	 [btrtl]
  h5_btrtl_setup+0xd0/0x2f8 [hci_uart]
  h5_setup+0x50/0x80 [hci_uart]
  hci_uart_setup+0xd4/0x260 [hci_uart]
  hci_dev_open_sync+0x1cc/0xf68 [bluetooth]
  hci_dev_do_o...