net/cnxk: fix build with optimization

net/cnxk: fix build with optimization

Fix the following build error seen with --optimization=1 and
GCC 10.3.0.

drivers/net/cnxk/cnxk_ethdev_mtr.c: In function
‘cnxk_nix_mtr_policy_validate’:
lib/ethdev/rte_mtr_driver.h:188:10: error: ‘str’ may be used
uninitialized in this function [-Werror=maybe-uninitialized]

drivers/net/cnxk/cn10k_rx.h:149:2 error: ‘frag_ptr’ may be
used uninitialized in this function

Bugzilla ID: 939
Fixes: b526599020ef ("net/cnxk: fix build with GCC 12")
Cc: stable@dpdk.org
Reported-by: Ferruh Yigit <ferruh.yigit@intel.com>
Signed-off-by: Rakesh Kudurumalla <rkudurumalla@marvell.com>
Tested-by: Daxue Gao <daxuex.gao@intel.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>