ibmvnic: Ensure that CRQ entry read are correctly ordered

Ensure that received Command-Response Queue (CRQ) entries are
properly read in order by the driver. dma_rmb barrier has
been added before accessing the CRQ descriptor to ensure
the entire descriptor is read before processing.

Fixes: 032c5e82

 ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: Lijun Pan <ljp@linux.ibm.com>
Link: https://lore.kernel.org/r/20210128013442.88319-1-ljp@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>