igb: Fix for improper allocation flag in igb_get_i2c_client

This patch fixes the allocation function in igb_get_i2c_client to use
GFP_ATOMIC instead of GFP_KERNEL because we have a spinlock.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Carolyn Wyborny <carolyn.wyborny@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>