Struct mlx4_vhcr was implicitly padded by the gcc compiler on 64-bit
architectures.

This commit makes that padding explicit, to prevent issues with
changing compilers and with incompatibilities between 32-bit architecture
implicit padding and 64-bit architecture implicit padding.

This structure is used in virtualization for communication between
the Host and its Guests. The explicit padding allows 64-bit Hosts
(old and new) to continue to interoperate with 64-bit Guests (old and new).

However, without this fix, 64-bit Hosts could not interoperate with 32-bit
Guests (since these did not insert the padding dword). With this fix,
32-bit Guests will be able to interoperate with 64-bit Hosts (since
the structure offsets will be identical on both).
Reported-by: Alexander Schmidt <alexs@linux.vnet.ibm.com>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>