qed: Fix static checker warnings.

Static checker warnings:
drivers/net/ethernet/qlogic/qed/qed_int.c:2450 qed_init_cau_sb_entry()
warn: always true condition '(cdev->rx_coalesce_usecs <= 255) =>
(0-255 <= 255)'
drivers/net/ethernet/qlogic/qed/qed_int.c:2511 qed_int_cau_conf_sb()
warn: always true condition '(p_hwfn->cdev->rx_coalesce_usecs <= 255)
=> (0-255 <= 255)'
..

The data types for rx/tx_coalesce_usecs should be u16.

Fixes: commit 722003ac ("qed: Add support for coalescing config read/update.")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sudarsana Reddy Kalluru <sudarsana.kalluru@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>