cxgb4i: don't redefine DIV_ROUND_UP

let's use the common definition to avoid the following warning during the
compilation:

drivers/scsi/cxgbi/cxgb4i/cxgb4i.c:161:0: warning: "DIV_ROUND_UP" redefined
 #define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
 ^
In file included from include/linux/list.h:8:0,
                 from include/linux/module.h:9,
                 from drivers/scsi/cxgbi/cxgb4i/cxgb4i.c:16:
include/linux/kernel.h:67:0: note: this is the location of the previous definition
 #define DIV_ROUND_UP __KERNEL_DIV_ROUND_UP
 ^

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>