mwifiex: remove redundant scan operation

It should have been removed by commit "mwifiex: use cfg80211 dynamic
scan..." (7c6fa2a843..) after adding code to avoid an extra scan
during association because scan entries are valid for 15 seconds in
cfg80211 stack.

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>