bnxt_en: Need memory barrier when processing the completion ring.

bnxt_en: Need memory barrier when processing the completion ring.

Orabug: 23221795

The code determines if the next ring entry is valid before proceeding
further to read the rest of the entry.  The CPU can re-order and read
the rest of the entry first, possibly reading a stale entry, if DMA
of a new entry happens right after reading it.  This issue can be
readily seen on a ppc64 system, causing it to crash.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 67a95e2022c7f0405408fb1f910283785ece354a)
Signed-off-by: Brian Maly <brian.maly@oracle.com>