S2io: Check for register initialization completion before accesing device registers

- Making sure register initialisation is complete before proceeding further.
  The driver must wait until initialization is complete before attempting to
  access any other device registers.

Signed-off-by: Surjit Reang <surjit.reang@neterion.com>
Signed-off-by: Sreenivasa Honnur <sreenivasa.honnur@neterion.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>