net/ice/base: fix build with GCC 12

net/ice/base: fix build with GCC 12

GCC 12 with -O2 flag would raise the following warning:
../drivers/net/ice/base/ice_switch.c:7220:61: error: writing 1 byte into a
region of size 0 [-Werror=stringop-overflow=]
 7220 |           buf[recps].content.lkup_indx[i + 1] = entry->fv_idx[i];
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~

This patch changed the type of fv_idx in struct ice_recp_grp_entry to
align with its callers which are also u8 type.

Fixes: 04b8ec1ea807 ("net/ice/base: add protocol structures and defines")
Cc: stable@dpdk.org
Signed-off-by: Wenxuan Wu <wenxuanx.wu@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>