mwifiex: correct packet length for packets from SDIO interface

While receiving a packet on SDIO interface, we allocate skb with
size multiple of SDIO block size. We need to resize this skb
after RX using packet length from RX header.

Cc: <stable@vger.kernel.org>
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>