net/hns3: fix build with SVE

net/hns3: fix build with SVE

Building with SVE extension enabled stopped with error:

 error: ACLE function ‘svwhilelt_b64_s32’ requires ISA extension ‘sve’
   18 | #define PG64_256BIT  svwhilelt_b64(0, 4)

This is caused by unintentional cflags reset.
Fixed the issue by not touching cflags, and using flags defined by
compiler.

Fixes: 952ebacce4f2 ("net/hns3: support SVE Rx")
Cc: stable@dpdk.org
Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>