net/enic: fix completion pointer calculation

net/enic: fix completion pointer calculation

The completion queue index could be implicitly extended past its
uint16_t size when multiplied by the size of the descriptor. While
this should not be a problem, coverity flags it. Do the extension
explicitly by casting the index to uintptr_t.

Coverity issue: 161317
Fixes: 8b428cb5a92e ("net/enic: use 64B completion queue entries if available")
Cc: stable@dpdk.org
Signed-off-by: John Daley <johndale@cisco.com>
Reviewed-by: Hyong Youb Kim <hyonkim@cisco.com>