mwifiex: update config_bands during infra association

Currently "adapter->config_bands" is updated during infra
association only if channel is provided by user in "iw connect"
command. config_bands is used while preparing association
request to calculate supported rates by intersecting our rates
with the rates advertised by AP.

There is corner case in which we include zero rates in
supported rates TLV based on previous IBSS network history,
which leads to association failure.

This patch fixes the problem by correctly updating config_bands.

Cc: "3.7.y" <stable@vger.kernel.org>
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>