IB/ehca: Repoll CQ on invalid opcode

When the ehca driver detects an invalid opcode in a CQE, it currently
passes the CQE to the application and returns with success. This patch
changes the CQE handling to discard CQEs with invalid opcodes and to
continue reading the next CQE from the CQ.

Signed-off-by: Alexander Schmidt <alexs@linux.vnet.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>