scsi: cxgb4i: Fix dereference of pointer tdata before it is null checked

scsi: cxgb4i: Fix dereference of pointer tdata before it is null checked

Currently pointer tdata is being dereferenced on the initialization of
pointer skb before tdata is null checked. This could lead to a potential
null pointer dereference.  Fix this by dereferencing tdata after tdata has
been null pointer sanity checked.

Link: https://lore.kernel.org/r/20200709135217.1408105-1-colin.king@canonical.com
Fixes: e33c2482289b ("scsi: cxgb4i: Add support for iSCSI segmentation offload")
Addresses-Coverity: ("Dereference before null check")
Acked-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>