mwifiex: change hscfg gap parameter to avoid potential firmware deadlock

If host sleep parameter gap is set to 0xff, firmware will wait
for an ack from host to confirm the success of host wakeup.
This prevents firmware from uploading data packet before host
actually wakes up.

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