mtd: elbc nand: use drvdata to only remove the relevant chip

Previously the remove method was looping and removing all chips,
which is obviously not the right thing to do — left over from when
the driver was organized differently and that was the remove method for
the entire controller.  This would result in bad things happening if
you have more than one NAND chip, and remove the module.

This also fixes priv->dev to properly point to the chip's device rather than
the controller's.  Until now priv->dev was only used for error/debug prints
(and it's an improvement there), so this shouldn't break anything.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>