brcm80211: smac: remove usage of brcmu_pkttotlen

The function brcmu_pkttotlen calculates the total length of a sk_buff
chain following the next pointer. In brcmsmac this is not needed as
in each place where it was used the provided sk_buff had a NULL pointer
as next field value.

Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>