scsi: fnic: Remove a useless struct mempool forward declaration

struct mempool doesn't currently exist, and thus also isn't used in
fnic.h, remove it.

Signed-off-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Karan Tilak Kumar <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/fnic/fnic.h

···
 	FNIC_IN_ETH_TRANS_FC_MODE,
 };
 
-struct mempool;
-
 enum fnic_role_e {
 	FNIC_ROLE_FCP_INITIATOR = 0,
 };