wil6210: use kfree_skb() instead of kfree()

Use kfree_skb() instead of kfree() to free sk_buff.

Introduced by commit e270045b569cc7030abd29857f3a4e7906524ec0
(wil6210: Sanity check for reported DMA length)

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Git-commit: 110dea0008c40a20f1ce280b636f87fff58a7403
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Liron Kuch <lkuch@codeaurora.org>