ixgbe: Correct length check for round up

The function ixgbe_host_interface_command actually uses a multiple
of word sized buffer to do its business, but only checks against
the actual length passed in. This means that on read operations it
could be possible to modify locations beyond the length passed in.
Change the check to round up in the same way, just to avoid any
possible hazard.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>