ixgbe: Use true, false for bool variable in __ixgbe_enable_sriov()

Fix the following coccicheck warning:

drivers/net/ethernet/intel/ixgbe/ixgbe_sriov.c:105:2-38: WARNING:
Assignment of 0/1 to bool variable

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>