brcm80211: fmac: add function to free the glom skb queue

In several places in dhd_sdio.c a skb packet queue was being emptied
and the packets freed. This warrants to have a function in place to
do this.

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