net: ena: fix compilation error in xtensa architecture

net: ena: fix compilation error in xtensa architecture

BugLink: http://bugs.launchpad.net/bugs/1798182
linux/prefetch.h is never explicitly included in ena_com, although
functions from it, such as prefetchw(), are used throughout ena_com.
This is an inclusion bug, and we fix it here by explicitly including
linux/prefetch.h. The bug was exposed when the driver was compiled
for the xtensa architecture.

Fixes: 689b2bdaaa14 ("net: ena: add functions for handling Low Latency Queues in ena_com")
Fixes: 8c590f977638 ("ena: Fix Kconfig dependency on X86")
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 00f17a8219f02139119d8b4547e032bf4888fa0d net-next)
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>