[SCSI] libfcoe: Fix incorrect MAC address clearing

Fix typo in memset. Incorrect length parameter to memset resulting non-zero MAC address in FPMA messages.

Signed-off-by: Kaladhar Musunuru <kmusunuru@juniper.net>
Acked-by: Joe Eykholt <jeykholt@cisco.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>