mwifiex: improvement in cfg80211 set_bitrate_mask handler

This patch configures data rates to firmware using bitrate mask
provided by cfg80211.

Earlier we used to only update band information in this handler
which will be used later for ibss network. Due to recent
modifications in ibss join code we don't need to do that.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Avinash Patil <patila@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>