mwifiex: make mwifiex_insert_cmd_to_free_q local static

after factoring out mwifiex_cancel_pending_scan_cmd
the function is not called outside of cmdevt file
moved function to head of file to avoid forward declaration,
also moved mwifiex_recycle_cmd_node since they are very similar

Signed-off-by: Andreas Fenkart <afenkart@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>