scsi: libcxgbi: Remove an unused field in struct cxgbi_device

scsi: libcxgbi: Remove an unused field in struct cxgbi_device

Usage of .dev_ddp_cleanup() in libcxgbi was removed by commit 5999299f1ce9
("cxgb3i,cxgb4i,libcxgbi: remove iSCSI DDP support") on 2016-07.

.csk_rx_pdu_ready() and debugfs_root have apparently never been used since
introduction by commit 9ba682f01e2f ("[SCSI] libcxgbi: common library for
cxgb3i and cxgb4i")

Remove the now unused function pointer from struct cxgbi_device.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/58f77f690d85e2c653447e3e3fc4f8d3c3ce8563.1725223504.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>