mwifiex: process RX packets in SDIO IRQ thread directly

ksdioirqd has higher priority than kworker. Process RX packets
in SDIO IRQ thread (ksdioirqd/mmcX) directly instead of deferring
the work to kworker to avoid the extra latency.
This improves TCP throughput 15~20% on an ARM platform with SDIO
2.0 controller.

Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>