mempool/dpaa2: fix error code for allocation failure

mempool/dpaa2: fix error code for allocation failure

In case the alloc api is not able to allocate the required
number of buffer, it can return '0', which will not indicate
the failure to the calling function.
This patch fix the return value to indicate the failure.

Fixes: 5dc43d22b5ad ("mempool/dpaa2: add hardware offloaded mempool")
Cc: stable@dpdk.org
Signed-off-by: Hemant Agrawal <hemant.agrawal@nxp.com>
Reviewed-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Shreyansh Jain <shreyansh.jain@nxp.com>