igb: Fix for lockdep issue in igb_get_i2c_client

This patch fixes a lockdep warning in igb_get_i2c_client by
refactoring the initialization and usage of the i2c_client
completely.  There is no on the fly allocation of the single
client needed today.

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>