[SCSI] fnic: fix memory leak

Fix memory leak arising due to incorrect freeing of allocated memory
for vnic stats when unregistering a vnic.

Signed-off-by: Abhijeet Joglekar <abjoglek@cisco.com>
Signed-off-by: Venkata Siva Vijayendra Bhamidipati <vbhamidi@cisco.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>