mwifiex: fix cmd and Tx data timeout issue for PCIe cards

We are sending sleep confirm done interrupt in the middle of
sleep handshake. There is a corner case when Tx done interrupt
is received from firmware during sleep handshake due to which
host and firmware power states go out of sync causing cmd and
Tx data timeout problem.

Hence sleep confirm done interrupt is sent at the end of sleep
handshake to fix the problem.

Cc: <stable@vger.kernel.org> # 3.10+
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>