examples/ip_pipeline: fix memory allocation check

examples/ip_pipeline: fix memory allocation check

Static analysis shows that once instance of rte_zmalloc is missing
a return value check in the code. This is fixed by adding a return
value check. The malloc call itself is moved to earlier in the function
so that no work is done unless all memory allocation requests have
succeeded - thereby removing the need for rollback on error.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>