mwifiex: check for bss_role instead of bss_mode for STA operations

This patch fixes an issue wherein association would fail on P2P
interfaces. This happened because we are checking priv->mode
against NL80211_IFTYPE_STATION. While this check is correct for
infrastructure stations, it would fail P2P clients for which mode
is NL80211_IFTYPE_P2P_CLIENT.

Better check would be bss_role which has only 2 values: STA/AP.

Cc: <stable@vger.kernel.org> # 3.10.y
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Stone Piao <piaoyun@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>