ixgbe: Use function pointer for ixgbe_acquire/release_swfw_sync()

Change remaining direct calls to function pointers.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Evan Swanson <evan.swanson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>