mempool/octeontx2: fix build with icc

mempool/octeontx2: fix build with icc

The Intel compiler is pickier about casts and generates:
otx2_mempool_ops.c(344):
     error #191: type qualifier is meaningless on cast type
  	int64_t * const addr = (int64_t * const)
  	                        ^
This is because of the nature of const.
In this example, the expression is being cast into a pointer
that can not be modified. This is meaningless because the
expression is already a lvalue.

See https://en.wikipedia.org/wiki/Const_(computer_programming)

Fixes: d7a0da3c0043 ("mempool/octeontx2: add fast path mempool ops")

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>