igb: use ARRAY_SIZE to replace calculating sizeof(a)/sizeof(a[0])

igb: use ARRAY_SIZE to replace calculating sizeof(a)/sizeof(a[0])

Use the ARRAY_SIZE macro rather than calculating sizeof(a)/sizeof(a[0]).
Also directly replace the code rather than using an unnecessary define.

Reported-by: Maninder Singh <maninder1.s@samsung.com>
Reported-by: Joe Perches <joe@perches.com>
Signed-off-by: Todd Fujinaka <todd.fujinaka@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>