igc: Assign boolean values to a bool variable

Fix the following coccicheck warnings:

./drivers/net/ethernet/intel/igc/igc_main.c:4961:2-14: WARNING:
Assignment of 0/1 to bool variable.

./drivers/net/ethernet/intel/igc/igc_main.c:4955:2-14: WARNING:
Assignment of 0/1 to bool variable.

./drivers/net/ethernet/intel/igc/igc_main.c:4933:1-13: WARNING:
Assignment of 0/1 to bool variable.

./drivers/net/ethernet/intel/igc/igc_main.c:4592:1-24: WARNING:
Assignment of 0/1 to bool variable.

./drivers/net/ethernet/intel/igc/igc_main.c:4438:2-25: WARNING:
Assignment of 0/1 to bool variable.

./drivers/net/ethernet/intel/igc/igc_main.c:4396:2-25: WARNING:
Assignment of 0/1 to bool variable.

./drivers/net/ethernet/intel/igc/igc_main.c:4018:2-25: WARNING:
Assignment of 0/1 to bool variable.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Zhong <abaci-bugfix@linux.alibaba.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>