mfd: max77693: Init max77693->dev before using it

Current code uses max77693->dev in the dev_err call before setting it to
&i2c->dev. Fix it.

This patch also includes below cleanups:
 - Move checking pdata earlier and show dev_err if no platform data found.
 - Remove unnecessary err_regmap goto label.
 - Unregister i2c devices if regmap init for muic fails.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>