ixgbe: Clean up interface for firmware commands

ixgbe: Clean up interface for firmware commands

Clean up the interface for issuing firmware commands to use a
void * instead of a u32 *. This eliminates a number of casts.
Also clean up ixgbe_host_interface_command in a few other ways,
eliminating comparisons with 0, redundant parens and minor
formatting issues.

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>