qla2xxx: Reset reserved field in firmware options to 0

During NVRAM initialization in target mode, reset reserved
fields in firmware options to Zero (BIT 15)

Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Giridhar Malavali <giridhar.malavali@cavium.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>