target/cxgbit: Fix endianness annotations

This patch does not change any functionality but avoids that sparse
complains about endianness.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Acked-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>