qed: Fix qed_ll2_post_rx_buffer_notify_fw() by adding a write memory barrier

[ Upstream commit 46721c3d9e273aea880e9ff835b0e1271e1cd2fb ]

Make sure chain element is updated before ringing the doorbell.

Signed-off-by: Denis Bolotin <dbolotin@marvell.com>
Signed-off-by: Ariel Elior <aelior@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>