mwifiex: fix issues in band configuration code

Currently due to following issues in the code even if device is
configured in B only, G only or BG mode using iw bitrates command,
ibss is getting created in BGN mode.

1) mwifiex_channels_to_cfg80211_channel_type() routine gives channel
type as NL80211_CHAN_HT20 for non-HT channel as well, because driver
doesn't store HT information provided by stack for the channel.
This issue is fixed by maintaining channel type information in
'adapter->channel_type'.
2) Band configuration is unnecessarily overwritten with BGN/AN while
setting channel.

This patch makes sure that "adapter->config_bands" correctly gets
modified while setting channel.

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>