mempool/octeontx2: fix build

mempool/octeontx2: fix build

Change the definition of C99 style to C90 style.
compile log as below:

otx2_mempool_ops.c: In function ‘otx2_npa_populate’:
drivers/mempool/octeontx2/otx2_mempool_ops.c:790:2: error:
	‘for’ loop initial declarations are only allowed in C99 mode
  for (int i = 0; i < OTX2_L1D_NB_SETS; i++)
  ^
drivers/mempool/octeontx2/otx2_mempool_ops.c:790:2:
	note: use option -std=c99 or -std=gnu99 to compile your code

Fixes: 9ed8e95c ("mempool/octeontx2: optimize for L1D cache architecture")

Signed-off-by: Tao Zhu <taox.zhu@intel.com>
Reviewed-by: Jerin Jacob <jerinj@marvell.com>