mwifiex: fix bugs in event handling code

This patch ensures uniformity in event skb sent by interface code
(USB/PCIe/SDIO) which automatically fixes following bugs.

1) For USB interface, same buffer is reused for receiving cmd and
events from firmware. While handling events, we perform
skb_pull(skb, 4) to remove event header. Corresponding skb_push()
call is missing while submitting the buffer.
2) For PCIe interface, event skb is passed with event header.
Recently added uAP events EVENT_UAP_STA_ASSOC, EVENT_UAP_STA_DEAUTH
will not work for PCIe, as they assume event skb points to event body.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kiran Divekar <dkiran@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>