staging: wilc1000: use mutex instead of struct semaphore hSemScanReq

This patch replaces struct semaphore hSemScanReq with struct mutex
scan_req_lock. It is better to use mutex than semaphore.

Signed-off-by: Chaehyun Lim <chaehyun.lim@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>