fore200e: fix missing unlock on error in bsq_audit()

Add the missing unlock before return from function bsq_audit()
in the error handling case.

Fixes: 1d9d8be9 ("fore200e: check for dma mapping failures")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>