bluetooth/controller: Update paths in inclusions of nrfx HAL files

After nrfx glue code was decoupled from nrfx sources, it is no longer
feasible to use those inclusions in the <nrfx/hal/nrf_*.h> form (there
is no point in adding the main directory of the hal_nordic module as
an include path solely for this reason). Remove then the nrfx/ part.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>