staging: brcm80211: remove unneccessary packets funtion prototype

The prototype for function pktsegcnt in bmcutils.h is not defined
nor used anywhere in the driver so it can be removed.

Reviewed-by: Brett Rudley <brudley@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>