OMAP: DSS2: PicoDLP: fix error handling in power_on

Fix two problems in PicoDLP driver's error handling on
picodlp_panel_power_on:

- If omapdss_dpi_display_enable() failed, the its error value was not
  returned
- If picodlp_i2c_init() failed, dssdev->state was erroneously set to
  OMAP_DSS_DISPLAY_ACTIVE

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>