staging: brcm80211: stop using assigned thread priority in fullmac

Stop assigning priority to watchdog and dpc threads. Remove related
code.

Reviewed-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>