staging: brcm80211: move assert function to dhd_linux.c

staging: brcm80211: move assert function to dhd_linux.c

The source file wl_iw.c is primarily intended to provide wireless
extensions functionality, which is to be removed from the driver.
The assert function is moved to another source file.

Signed-off-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>