mwifiex: remove unreachable code

In disconnected state "iw dev mlan0 link" command will return
from cfg80211 stack itself. We also have an error check in
mwifiex_cfg80211_get_station() routine. Therefore the code
under "if (!priv->media_connected)" condition in
mwifiex_rate_ioctl_get_rate_value() routine becomes unreachable.

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>