mwifiex: use bss_type and bss_num to retrieve priv

mwifiex: use bss_type and bss_num to retrieve priv

Current implementation, for retrieving priv from adapter,
uses bss_index. In multi interface environment supporting
different types, bss_index may not be unique.

Use bss_type along with bss_num to retrieve the priv.
bss_index is removed with this change.

Signed-off-by: Yogesh Ashok Powar <yogeshp@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>