mwifiex: remove redundant variable scan_table_idx

mwifiex_get_bss_info() routine updates variable 'info->scan_table_idx'
but it is never used.

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>