net/i40e/base: fix compile issue for GCC 6.3

net/i40e/base: fix compile issue for GCC 6.3

When using GCC 6.3.0 and EXTRA_CFLAGS=-Og, the compiler is not smart
enough to see that when you have an integrated VF that just one of the
if statemets has to be true so that ntu is always set. Fix the way that
the code is for integrated VFs so that the compiler won't complain.

Fixes: 9783eb15eb98 ("i40e/base: wrap the register definitions for PF and VF")
Cc: stable@dpdk.org
Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
Acked-by: Beilei Xing <beilei.xing@intel.com>