bluetooth: controller: Fix build with BT_HCI_VS_EXT disabled

[216/319] Building C object zephyr/subsys/bluetooth/controller/
  CMakeFiles/subsys__bluetooth__controller.dir/hci/hci.c.obj
zephyrproject/zephyr/subsys/bluetooth/controller/hci/hci.c:
   In function 'hci_vendor_cmd_handle_common':
zephyrproject/zephyr/subsys/bluetooth/controller/hci/hci.c:5459:17:
   warning: implicit declaration of function 'vs_set_min_used_chans';
   did you mean 'll_set_min_used_chans'? [-Wimplicit-function-declaration]
 5459 |                 vs_set_min_used_chans(cmd, evt);
      |                 ^~~~~~~~~~~~~~~~~~~~~
      |                 ll_set_min_used_chans
....
zephyr-sdk-0.15.0/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.1.0/../
  ../../../arm-zephyr-eabi/bin/ld.exe: zephyr/subsys/bluetooth/controller/
  libsubsys__bluetooth__controller.a(hci.c.obj): in function
   `hci_vendor_cmd_handle_common':
zephyrproject/zephyr/subsys/bluetooth/controller/hci/hci.c:5459: undefined
   reference to `vs_set_min_used_chans'
collect2.exe: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

Signed-off-by: Szymon Janc <szymon.janc@codecoup.pl>