Bluetooth: PACS: Fix logical dead paths

In pac_notify and pac_notify_loc coverity found logical dead
paths since if both sink and source notify was disabled,
the functions would still be compiled, but would
never get past the default case.

This is not a real issue as the functions were never called
in that case, but to make coverity happy, and to prevent
any future issues where the functions may be called
incorrectly, the static functions are now fully guarded.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>